How do you replace the relief valve on a water heater?

To replace the relief valve on a water heater, first, turn off the power or gas supply and shut off the cold water supply to the heater. Next, drain some water from the tank to relieve pressure, then use a wrench to unscrew the old relief valve from its socket. Install the new valve by threading it into the socket and tightening it securely, then restore the water supply and check for leaks before turning the power or gas back on.