Unplug the microwave from the wall outlet, or turn off the breaker in your service panel.
Remove the screw located on the side of the light cover, then lower the cover. The cover has hinges on the side and does not completely separate from the microwave.
Pull the light bulb out of the light socket and discard.
Insert the new light bulb fully into the light socket. Be sure to wear gloves when handling the light bulb.
Lift the light cover and reattach it using the screw that was removed.
Restore the microwave's power supply.