Diagnosis
The light bulb is a halogen type (part number WB27X11032) and is accessed from inside the microwave cavity, not from the top or bottom.
How to Fix It
Unplug the microwave. Look at the top interior ceiling of the cooking cavity. You'll see a clear plastic lens cover. Press the small tab on one side of the lens and swing it down. The bulb is now exposed. Pull the old bulb straight out. Push the new bulb in. Snap the lens cover back into place.
If That Didn't Work
If the new bulb doesn't light, the issue could be the light socket or the control board relay. Test for power at the socket contacts with a multimeter when the light button is pressed.
Heads Up
Use only the specified halogen bulb. A higher wattage bulb can overheat and damage the socket or lens. Handle the bulb with a cloth to avoid skin oils shortening its life.