I am currently renting a condo that the landlord had bought replacement knobs for the shower before moving, but didn't have time to install them. He is out of state. I tried putting them on but they were the wrong ones and I happened to strip the brass parts that the knobs tighten up to. When I went to home depot I was told 2 different things, one of which is that I would have to get behind the wall and replace the whole thing, and another answer of that I can replace the stems with out going behind the wall. The only way to turn the hot and cold watter off is to use pliars but now it is getting so stripped that the hot water always drips and it is getting harder and harder to turn off completley. I am ready to replace them but do not know what it will take. I was advised at one point that I can remove part of it and there are replacements of the stems that come with knobs if needed. I need to do something about this soon, can anyone help on this?

I guess you waited too long to do something about it, if you are now using pliers. I would suggest you get a plumber to look at it for you and get it over and done with.

If you have the knobs off, you should be able to see a hex, or maybe a round disk with 2 flat sides. Shut the water off at the stops or the water meter, and unscrew them. Take them to a real hardware store, Ace, True Value, etc. A good one will have somebody that can help you match the old ones to new ones. If they don't come with knobs, buy ones that fit. Note, hot and cold turn different directions and need different stem assemblies. Also make sure the seat the assembly seals against is smooth or they will leak. Better faucets have replaceable ones.