Turn off the water supply
Open the faucet to drain remaining water
Remove the shower handle and trim plate
Remove the old valve access cover if needed
Disconnect the old valve from the water lines
Measure and mark the correct valve height and depth
Install the new valve in the wall framing
Secure the valve with screws or brackets
Connect the hot and cold water lines
Connect the shower outlet and tub spout line if applicable
Solder, crimp, or tighten fittings as required by the valve type
Check that the valve is level and properly aligned
Turn the water supply back on briefly to test for leaks
Shut the water off again if leaks are found
Flush the lines before installing the trim
Install the escutcheon plate and handle
Restore the wall surface around the valve opening
Test the shower valve operation and temperature control