My unit had to be removed from the wall cabinet before getting to anything that other posts covered. BASIC DESIGN FLAW--GE did not provide an easy access panel inside the microwave for bulb replacement...instead the outer shell must be removed to do the job. And to complicate removing that shell, GE used a few "security" screws...TT-20 not available at my Lowes or Home Depot.
The job is easy, but it's not an under 15 minute job.
Get the security screw tip BEFORE starting the job. ;-)