Ceramic or other hard wall tiles are often more difficult to remove than floor tiles, because walls are more fragile than floors. With a floor, you can take a sledge hammer to the ceramic if all else fails; try that on a wall, and you'll be looking into the next room. Patience and persistence are needed to get tiles off a wall (along with a grout saw, hammer and chisel).
Removing Single Tiles
If you've got a cracked or broken tile, or group of tiles, and you want to remove just those tiles so they can be replaced, start with the grout. Grout lines aren't as hard as the tiles themselves, and if you can get some of the grout out, you can get behind the tile to pry it off. Use a grout saw, which looks like a thick razor blade on the end of a handle, to scrape at the grout until it crumbles out of the lines. Then use a hammer and sharp chisel to gently tap at the base of the expose tile, separating it from the wall.
Removing All the Tiles
If all the tile on the wall has to come out, your project is actually a little easier than if you're just pulling out one or two, because you don't have to be careful about not damaging adjacent tiles. Start as in Section 1, digging out grout to get between two tiles, then just chisel under all the tiles from there and knock them down. You'll want to wear eye protection because of flying shards of ceramic, and lay a thick canvas tarp under the area so the falling tiles don't damage the floor.
Removing the Adhesive
After the tiles are gone, you'll be left with some of the adhesive that was used to hang it, and that will have to come off as well. If the tile was hung with thinset mortar, then use a sharp, wide chisel and hammer to tap it off. It should break like loose cement. Follow up by belt-sanding the wall smooth. If the tile was hung with pliable chemical adhesive, soak it with tile adhesive remover from your hardware store, let the remover soften up the adhesive for a few minutes, then scrape it all off with a razor-scraper.