if it's ceramic/porcelain, go to home depot. Rent a hilti jackhammer with 2 different bits (they'll know which ones to give you). one is a narrow chisel that pops the tiles up. the other is a wide blade that will remove thinset. sometimes the wide blade works good for removing the tile, also. whichever works best for YOU. They will explain how to use it. It is WAY easy to use and you will NOT regret it! You will want to plastic off areas that you are not removing tile completely, there will be dust. good luck! don't be cheap and buy the handscraper! you'll hate yourself.
There is a powered floor scrapper that can be rented. You have to buy the blade but it isn't that expensive. Most good tool rentals have them.
How to remove a tile? First of all, get a good old chisel and hammer. You have to break the tiles and remove the plaster. Just be careful you do not over do it or you will end up damaging the wall totally. Safety is also a concern. When you chisel or break these tiles, sharp pieces of it becomes a dangerous projectile scattering all over. Always wear protective gear, like glasses, gloves and a mask if you are allergic to dust. Off course if there is a drain nearby, cover it to prevent dust or tile particles from entering the drain.
