Open the cabinet doors above the microwave and unplug the unit.
Ask a helper to hold the bottom of the microwave. Turn the screws in the bottom of the cabinet counter-clockwise to loosen them. When they are loose, pull them out and set them aside.
Ask your helper to tilt the microwave slightly forward.
Place your hands at the back of the microwave and press up firmly on the side closest to you until the microwave's back panel lifts up and out of the wall mount's tab.
Push upward on the far side of the appliance in a similar manner until the back panel is removed from the mount's tab. Set the microwave aside.
Lift the microwave with the help of another person. Hold the microwave flush against the wall and the bottom of the cabinet just above it.
Slowly move the microwave slightly downward until the tabs on the wall mount slip into the microwave's back panel.
Place the screws back into the holes at the bottom of the cabinet while your helper continues to hold the microwave from the bottom.
Turn the screws clockwise until they connect the bottom of the cabinet to the top of the microwave with no wiggle room.