Unless there is an access panel you will have to go through the wall and the tile will be destroyed. If the tiles are older, then they might not be available in the same color pattern. Look behind the shower in a closet or on the wall for an access. Also depending what the wall is behind the shower (if no access is available)it might be easier - not mention cheaper - to go through that wall for a repair.
I just went through this with a tub surround. I ended up tearing out the whole tub surround and completely redoing it. While this is a lot of work at least I know its now done right!