Before you begin, safety first! Completely shut off the main water supply to your house. Then, turn on the shower faucet to relieve any remaining pressure. This prevents flooding during the repair.

Carefully remove the shower handle and the escutcheon plate covering the valve. This may involve unscrewing or gently prying them off. Use a utility knife to carefully cut any caulk or sealant if necessary.

Identify your valve type and its retaining mechanism (screws, clips, or retaining nut). Carefully remove the retaining mechanism and gently extract the old valve. If you have copper pipes and are uncomfortable soldering, opt for a compression fitting replacement valve.

Install the new shower valve, using compression fittings if possible. Ensure proper alignment and securely tighten the compression nuts. If soldering is needed and you lack experience, call a licensed plumber. Apply plumber's putty to the valve base for a watertight seal.

Reinstall the escutcheon plate and handle. Slowly turn the water supply back on and meticulously check all connections for leaks. Tighten fittings as needed and retest if necessary.