Unplug the power cord and ensure that the cord isn't touching the socket.
Wait approximately five minutes after you unplug the microwave before working on it.
Remove the vent cover by unscrewing it. Look inside the door, on the right side of the cooking area, to find it.
Unscrew the bulb and remove it. Screw in the new one, which can be found at any hardware store.
Reattach the vent cover.