Turn off the water supply to the shower
Open the faucet to release any remaining water
Cover the drain to catch small parts
Remove the faucet handle screw
Pull off the handle
Remove the trim plate
Unscrew the faucet cartridge or valve stem
Pull out the old faucet parts
Compare the new faucet parts with the old ones
Install the new cartridge or valve stem
Reattach the trim plate
Reinstall the handle
Turn the water supply back on
Test the faucet for leaks and proper operation