Turn off the water supply to the shower
Cover the drain to catch small parts
Remove the shower handle screw
Pull off the handle
Remove the trim plate and sleeve
Remove the cartridge retaining clip or bonnet nut
Pull the old cartridge straight out
Note the cartridge orientation
Inspect the valve body for debris or damage
Clean the valve body opening
Apply plumber’s grease to the new cartridge O-rings if needed
Insert the new cartridge in the same orientation
Reinstall the retaining clip or bonnet nut
Reinstall the sleeve and trim plate
Reinstall the handle
Turn the water supply back on
Test for leaks and proper temperature control