Rotate the gas cock knob on top of the heater's control box to the "OFF" setting and wait approximately 15 minutes for any lingering gas to evacuate.
Unfasten and remove the thermocouple, gas and burner tubes from the bottom of the heater's control box with a wrench.
Remove the screws which secure the access panel to the side of the water tank with a flathead screwdriver, then remove the panel to access the burner.
Pull the burner out of the access panel opening.
Twist the burner in a counterclockwise direction until it disconnects from the burner tube.
Twist the new burner in a clockwise direction onto the tip of the burner tube.
Insert the burner into the water heater, ensuring that the flat tip of the burner-side of the tube slides into the slotted opening of the tube's mounting bracket within the heater.
Tighten the thermocouple, gas and burner tubes to the control box with a wrench.
Rotate the gas cock knob on top of the control box to the "PILOT" setting, then light a match and hold the flame next to the end of the gas tube. Press and hold down the "RESET" button on the control box until the pilot flame lights. Extinguish the match and hold the button down for approximately one minute. Turn the control knob to the "ON" setting and release the button.
Reattach the control panel to the side of the water tank with a flathead screwdriver.