Water leaking from hot and cold knobs in shower

Hello,
I just purchased a 3023 trailer in Texas. We checked everything out at the dealer except the shower. I didn't realize this until I closed the unit up at the dealer. I told we forgot to check the shower and he assured me the unit was checked top to bottom and it was good to go. My bad, we should of opened it up but I was in hurry and we been there for 3 hrs. Any way I popped it open in Tye Texas and spent the night at the campground. Well the dealer left 1/3 of a tank of water in the water tank so I decided check the shower. I turned on the water pump and opened both hot and cold water fixtures and water started streaming out from under the knobs. The good news is the water runs right down into the tub and the shower head works but I don't like the leak. Does anyone know how to fix this? Can I replace the stems or should I replace the whole fixture? If I replace the fixture how do access it? Any help would be appreciated. Thanks!

Eric Stone