Turn off the main water supply to the home with the shutoff valves, usually located in the basement near the water heater. Open the shower to empty any remaining water in the lines. Cover the drain with a cloth to prevent parts from falling down the drain.
Remove the single screw securing the faucet handle in place by unscrewing it with a flat head screwdriver. Loosen the screw on the escutcheon plate that is on the wall behind the faucet. Pull the escutcheon plate away from the wall.
Slide off the limit stop from the end of the valve. The limit stop controls the water temperature. Pop off the O-ring from the bottom off the limit stop with a flat head screwdriver. Use an adjustable wrench to unscrew the metal ring and turn it in a counterclockwise direction.
Lift the valve cartridge straight off the faucet. If the cartridge is difficult to remove, pry it off with a flat head screwdriver. Water may flow out of the faucet after the cartridge is removed. Clean up any water with a cloth.
Install the new valve cartridge by reversing the steps you completed to disassemble the faucet. Turn on the water supply to the shower faucet. Remove the cloth from the shower drain and test it.