If you are updating the fixtures in your bathtub or your bathtub handles have become worn or dingy, replacing them is a simple job. When buying new handles, make sure they will fit on the tub's faucet. It is a good idea to have your old handles with you when buying new ones.
Turn off the main water line to the bathtub. Open the handles to drain any water left in the pipes.
Unscrew the screw in the centre of the handles. There may be caps over these screws. If so, pop them off by prying carefully at the edge with a flathead screwdriver.
Firmly tug at the handles to pull them off of their stems. Wiggle as you pull if they are sticking. Lightly tap the back of the handles if necessary. Spray WD-40 into the screw hole and let it sit for a while if the handle is really stuck.
Check the rubber washers in the faucet unit. Pop them out with a flathead screwdriver. Replace them if they are worn.
Clean any gunk or corrosion from the faucet stem with baking soda and vinegar or another non-corrosive cleaning solution.
Attach the new handles by pushing them all the way onto the stems and screwing in the centre screw.
If you are replacing the entire faucet, ensure that the new faucet has stems that fit with the stem tree of the bathtub. The covers that fit over the faucet mechanisms can also be easily replaced.