Disconnect the power to the microwave by unplugging it from the wall, or by turning off the circuit breaker.
Open the microwave door, then unscrew and remove the two screws located on the vent grille. The vent grille is located on the top of the microwave, inside the area covered by the door when it is closed.
Slide the grille to the left, then tilt it forward. Lift the grille out of the microwave's frame to remove it.
Unscrew the mounting screw on the bulb holder, which is now exposed with the grille removed. Lift the bulb holder out of the microwave.
Remove the bulb from the bulb holder by unscrewing it from the base.
Insert a new 30-watt light bulb into the bulb holder, then replace the bulb holder and mounting screw. Replace the grille, securing it in place with the screws that were removed to complete the procedure.