Take off the faucet handle or handles by unscrewing the handle screws with an Allen wrench. The handle screws are located on top of each handle, or in the case of a single handle, beneath the handle's lever. Unscrew the old plate's screws with a screwdriver and pull the plate off. If you are changing out the old fixture for a new fixture, simply skip this step.
Apply silicone caulking for tubs and showers around the edges of the new remodeling plate. This seals the plate to your shower wall and prevents water from entering the interior of the wall.
Set the remodeling plate over the faucet body. Insert the screws into the mounting holes in the plate and thread them carefully into the housings on the body valve. Turn the screws clockwise to tighten them and secure the plate to the wall.