Given the amount of work involved, and the degree of difficulty, when you're looking at removing ceramic tiles on the wall or floor, give some consideration to whether you might be better off just replacing the cracked or damaged ones. Of course, if you can't get matching ones, that means doing the whole job over, but when you do, remember to buy enough tiles that you have extras, so that it won't need to be repeated again, should you ever have a couple of them damaged.
Before starting a removal job, decide whether you have anything there worth salvaging. It could be that while you want to redecorate the shower stall, that tile would like great on the wall in the laundry room. And it can be used over again, as long as you are careful in removing it. Ceramic tile has lots of compression strength, but very little tensile strength. That means you can put weight on it, but to twist or bend the piece, will likely break it.
First, you'll need to remove any trim that covers the edges of the tiles. Next, remove all the grout you can between the tiles. They're glued to your wall or floor, so nothing is going to fall off when you do this. But the grout must be removed, because in attaching them all together, it's like creating one giant sheet of ceramic, and it will be just as brittle as a single tile. So forcing one tile, can end up breaking a number of them.
Once the grout is cleaned away, take a very thin putty knife and start by working a corner under the edge of one tile. Work along the top, gradually inserting more of the blade as you go. You can use a hammer to gently tap the handle of the knife to help insert it. When the blade is about halfway down the back of the tile, you can exert slow, upward pressure, which should pop the tile off.
If you plan to re-use the tile, the backs will need to be cleaned, either with an adhesive remover, or by grinding, if they were applied with thinset.
Visit http://www.LearnHowToRemove.com for a growing library of tips to remove those annoying messes in your life.