Unplug the microwave's power cord from the wall outlet, which is often located in the cabinet above the microwave.
Remove the screw on the side of the light cover, securing the light cover to the underside of the microwave, and then lower the light cover. The light cover is hinged, and you can allow it to hang.
Pull the light bulb straight out of the socket, and then discard.
Align the terminals on the new light bulb and then fully insert it into the socket. Be sure to wear gloves whenever handling halogen light bulbs, as the oils from your fingers can shorten the life expectancy of the bulb.
Raise the light cover, and then secure it using the screw that you removed.
Plug the microwave back into the wall outlet.
Unplug the microwave's power cord from the wall outlet.
Remove the two screws securing the grill above the door to the microwave and then remove the grill.
Remove the charcoal filter if your model has one. To remove, slide the filter to the left, and then pull it straight out of the microwave.
Remove the lamp shield cover screw, and then pull the lamp shield cover out of the microwave.
Pull the light bulb out of the socket and discard.
Insert a new 120- or 130-volt, 20-watt halogen bulb into the light socket. Wear gloves when handling halogen light bulbs so as not to diminish the life expectancy of the bulb.
Replace the lamp shield and screw, and if applicable, the charcoal filter.
Replace the top grill, and then install the screws that you removed to secure it into position.
Plug the microwave back into the wall outlet.