I will say the same thing I said in the names(well almost). Heroes like Superman, Batman or Spiderman change their costumes but they always return to the original costume. Lesser known heroes tend to change their costumes, they haven't achieved an iconic status. For example She-Hulk changes her costume all the time, there is no costume that can be identified with her.

Depends on the hero Superman I would say should never change his costume 

New costume = bad.
New costume means a hero is going through an identity crisis.
MEANING. They either are attached to some strange power or have a change of heart.

Don't mean to be mean, but I found a few typos/misspellings in here.

" Don't mean to be mean, but I found a few typos/misspellings in here. "

Often costumes become outdated.
Imagine the X-men today in their original blue and yellow costumes.

" Often costumes become outdated. Imagine the X-men today in their original blue and yellow costumes. "

They change costumes because of their PR Reps... It's a marketing and licensing thing... That's how they get paid... 
  
Royalties 

I don't think it's a bad thing if it goes with a new story arch, such as spider-man/ symbiote.    I don't  mind if the costume stays the same but the colors change some, like x-men or x-force.   If a character is outdated and needs become modern or up to date I think that is ok too, such as Blade or Luke Cage.

"Often costumes become outdated. Imagine the X-men today in their original blue and yellow costumes. "

Have you guys seen Wolverines original costume? The one with whiskers?
Or Green Lanterns red, yellow &green one?
 
I have a bigger problem with how they re-write their origins and change their personalities willy-nilly.

As times change, so should costumes. Costumes from the early to mid 20th century don't hold up  in the 21st century.

I always like it when a costume change is done right and if it updates the character, like Iron Man's newest costume which is now my favourite. Or Ultimate captain America's slight change from Vol 1 to vol 2 to include new headgear.  
I loved the radical redesigns used in Kingdom come.  
Batman, Spider-man and Superman's costume have changed alot during the years. In subtle ways such as The symbol designs, the belts, and the colour schemes for batman. Spider-man's eyes have grown and these changes might have begun as Artist interpretations but have stuck due to their appeal.  
 
For super heroes that wear their costume everyday and who don't have any need to wear the costume such as gaining powers from it, then I cant see why they wouldnt have a change every once in a while. Wolverine seems to pick an outfit based on his mood or the mission, luke cage shows that some heroes dont even need a costume, and the Wasp showed that some people are more likely to want change. 

I don't mind costume changes, even drastic ones as long as it fits with the character's personality. Someone like Bruce isn't going to make a huge change to the bat suit other then maybe add a little more padding/armor here or there. Where someone like Janet, who was a fashion designer, wouldn't be caught dead in the same outfit for a long period of time. Now certain characters need to evolve with the times, like the Punisher at first he was in the black cloths with white gloves and boots and pretty much the same until Marvel Knights and Marvel MAX where he looked more modern and that leaked into the main 616, until they restarted his issues at Punisher.

yes, i think they should be able to update their costumes. They all have updated their costumes for the most part. Even tho it isnt mentioned and its more the artist variations they all have been updated. I would like to see acknowledged updates to costumes tho for people in DC. Marvel characters seem much easier to change their outfits, DC's costumes seem like they only get changes during or after big events (like the Death of Supergirl for Superman Earth-2)
 

I think in The Batman's case, the fewer changes have worked. It's an iconic costume that has been functional for a long time. Looking at most of the Golden Age costumes, they were all based off circus costumes. Aeriolists, highwire, strongmen, whatever. You look at Cary Grant or Burt Lancaster or somebody that started out in the circus and then went to hollywood, that's what they wore. 
 
Plus, Batman pretty much defines what a costume should do. It's should inspire some kind of reaction. Hope. Power. Fear. Or in Namor's or Wonder Woman's case hormones. (They run around in swimwear!)   
 
Spider-Man's costume is probably the single most original and innovative costume since the Golden Age. A lot of the Marvel costumes are. But, I'll give it to Spider-Man as the landmark. 
 
Wesley Dodds and Lee Travis should have stayed in their original costumes. they should never have changed costumes. That was when they became no different from other Mystery Men.  
    

"People" grow, and change. Their wardrobes reflect that, too. I think change can be a good thing. :) Look at Kitty Pryde. She's had numerous wardrobe changes throughout the decades, but remained the same kind, intelligent, and brave young woman on the inside.

As long as the character is still instantly recognizable, I don't think it's an issue Wolverine's costume has changed a ton of times. Whenever he's actually in a suit, his suit looks more or less the same, just different colors. When he's not in some kind of uniform, the whole hair in the shape of his helmet thing instantly identifies his as Wolvie.  
  
Same thing goes for Batman. As long as he has the cowl with the ears, he's Batman. Though, his costume changes have mostly been subtle.  
 
It's the same kind of thing. As long as the character's are still recognizable as themselves, I don't think it's an issue. 

its inevitable heroes will change their costume for various reasons. what works depends on the need. fluid versus manufactured. most of the time its fluid, to become more modern and less dorky, (i.e Aquamans orange shirt is more armour like now, robin lost the green undies and bright yellow cape, .) those kind of variations make sense and keep the spirit of the original. some are an example of changing times and fashion (dazzler went from skating disco ball in the 70s to jane fonda workout queen in the 80s ) the more manufactured changes are like armour spiderman or blue/red superman are blatant shakeups of old characters that can be self indulgent excesses of the writer or artist  and as you can see, most fans dont repond to it.      

I remember when Ben Reilly took over for Peter as Spider-man and everyone assumed he killed the original Spider-man just because his costume was different

You only forgave DAREDEVIL? What about Robin, im sure you can forgive Tim Drake and Damian Wayne for not sticking with the pixie/fish-scale speedo look right?

well, if a character changes his costume is usually for personal reasons. maybe he went through some form of trauma like when hawkeye became ronin, or maybe there was a crisis like when ms marvel changed. besides, costumes get torn up in fights and sometimes need replaced, what better time to update it? it doesn't bug me as long as i know who is under the mask.

"New costume = bad. New costume means a hero is going through an identity crisis. MEANING. They either are attached to some strange power or have a change of heart. "

I believe that, just like the name changes, a superhero should be allowed to change their costume.  Times change.  Motivations change.  Heroes change. 
I don't think they should be locked down to a single look, as it often means that their character isn't really changing or evolving. 
And that often means that a character has become stagnant, which is not a good thing.

I like a change now and then just to keep it new.  They don't have to do anything super drastic.  As characters have become more and more realistic in their portrayals it makes sense that they would want to occasionally make changes to their costumes.  As long as they are still recognizable, I think its great.  I think the most successful of all with having an alternate costume is Spider-Man.  I love both the red and blue and the black costumes.  Its fun to see him switch back and forth now and then.  It kind of emphasizes new chapters in his story.  Frequent updates/mutliple suits for Batman and Iron Man's suits just make sense with their characters.

I wish ALL heroes & villains would change their outfits... It's high time they wore something more than embarrassing figure-hugging spandex!

They all should be allowed to change costumes, but if they suck and the majority of the fans hate it, then they should change it back. Iconic characters are kind of stuck. I personally liked Wonder Woman's all white super agent costume better then her current one. Sadly I'm in the minority on that :'(

Of course they should be able to change their costumes.  It can add for all sorts of story elements.  If Spider-Man had never gotten his Black Costume, we never would have gotten Venom or Carnage. 
 
Wait... I'm now wondering if that was a good or bad thing.

A lot of the time it seems that they don't have a choice. Superman had to change because the suit stabilized his new powers. Spidey did the change because of the Secret War. Other times, heroes change because of what's going on in their lives at the time. Daredevil keeps changing because the dude's simply nuts. 

Hey I am the proud owner of the comic when Spider-Man first wore the symbiote

Nightwing had 4 different costumes and the last one was the best. Robin (all of them combined) had 6 different costumes. Sometimes costumes need to be updated with the times.

Yeah, heroes can change looks :) 
 
 except Superman :P 
 
Hes too Iconic

Hell yeah. As long as the alternate costumes are cool. XD