Open the kitchen cabinet just above the microwave. Find the power outlet into which the microwave is plugged. Pull the microwave cord from the outlet.
Insert the screwdriver into each of the screws that connect the bottom of the cabinet to the top of the appliance. Turn the screws counter-clockwise to loosen them. Make sure you have a helper stabilizing the bottom of the microwave as you remove the screws. Set the screws to the side after unscrewing each of the three screws.
Ask your helper to very slightly tilt the appliance forward toward himself. He should continue to hold the appliance in place.
Place your hand at the bottom of the back right corner of the microwave and strike it firmly with the palm of your hand to dislodge the small tab at the bottom of the wall mount from the small opening at the bottom of the microwave's back panel.
Move your hand to the opposite side of the microwave and repeat Step 4.
Keep both hands on the microwave as the appliance's back panel lifts up out of the wall mount's tabs, and set the microwave aside with the help of the person who has continued to hold the front of the appliance.
Pick up the new microwave. With the help of another person, lift the appliance straight up so that the top of it is flush against the bottom of the cabinet, and the back of it is flat against the wall mount.
Lower the microwave slightly so that the tabs at the bottom of the wall mount grab hold of the small insertion holes at the bottom of the microwave's back panel.
Ask your helper to press upward on the bottom of the microwave. While he presses upward, retrieve the screws you removed earlier and proceed to place them through the holes that are located in the bottom of your cabinet and the top of the appliance.
Use the screwdriver to tighten the screws.