In most cases you would have to remove the outer cover of the microwave, which means removing it from the wall.
In my professional opinion, no one should work on a microwave unless they are fully informed and aware of the deadly hazards and necessary precautions.
You can find this information and in our safety and disassembly text files at http://www.microwavedisplay.com
William Miller † MicrowaveDisplay.com, March 2007