Turn of the breaker that controls the electric current to the hot water heater. The breaker is located in the main fuse box, which is generally outside near your electric meter. Be sure to let anyone else in the house know not to turn the breaker back on while you are working.
Turn off the water supply to the hot water heater. The water supply knob is located near the floor at the back of the water heater on a pipe that is running into the heater.
Apply pipe sealer or teflon tape to the threads of the new drain valve to prepare it to be installed. Set it to the side.
Place a bucket under the faulty drain valve and open it to let water flow out. There will be a vacuum created by turning off the water supply and only a small amount of water should come out.
Remove the faulty drain valve with large pliers by grabbing it at the base and twisting hard to loosen it. Once it is loose, continue twisting with your hand until you pull it all the way out.
Push the new drain valve into place and turn it clockwise until it is screwed tightly into place. Turn the water supply knob back on and return power to the water heater.