Disconnect the Frigidaire professional microwave power cord from the AC wall outlet.
Open the microwave door and use a screwdriver to remove the screws on the vent cover over the top part of the unit.
Press down on the tabs holding the cover in place, then remove the cover from the microwave.
Use your hand to pull off the light bulb compartment. Twist the old light bulb counter-clockwise to remove it.
Discard the old light bulb, then twist the new light bulb clockwise into the microwave.
Push the light bulb compartment back into place and place the vent cover back onto the microwave.
Reinsert the screws into the cover, then close the door. Reconnect the power supply.