First all the films were made par Warner Bros.
But they have diffrent directors.
Batman and Batman Returns were par Tim Burton
link And it the same batsuit in both.
Now, Batman Forever and Batman & Robin were direct par Joel Schumacher
link and produced par Tim Burton
All this films are in the same universe and continuity. The change of batsuits is explained in the movies.
In Batman Forever the riddler destroys the batcave and the equipment, so Batman uses a new bat suit.
In Batman & Robin the change is just an upgrade for the batsuit.
Those changes in stylies were made par the director ou photographie i guess...but also many toys were sold thanks to that.
For plus go to:
link 
