Open the cabinet doors over the microwave to locate and unplug the power cord for the appliance.
Take out the screws inside the cabinet bottom where the hardware attaches to the top of the microwave, using a screwdriver. Have a friend hold the microwave in place from below.
Lift the microwave from the bottom to disengage the bracket on the back from the bracket bolted to the wall. Pull forward slowly, guiding the power cord downward from the hole in the underside of the cabinet.
Unscrew the metal support bracket from the wall.