Out With the Old
Remove everything from inside the wall cabinet that the existing microwave is attached to. Unplug the electrical cord from the wall.
Set the drill to "Reverse" and insert the Phillips-head drill bit into the drill. Remove all screws from the cabinet to detach the microwave from it. Have a friend hold the microwave during the process to avoid having it fall.
Lift the microwave from the wall bracket once the overhead screws are removed and set the microwave in a safe place on a flat surface.
Remove the screws from the wall using the drill and detach the bracket.
In With the New
Place the new wall bracket along the wall and see if any existing holes match up. If there are holes that do not match up, mark them on the wall with a pencil.
Drill through any new hole locations on the wall and insert a wall anchor into any holes that do not fall on a stud. This is determined by running the stud finder over the wall to locate studs.
Place the microwave bracket back on the wall, lining up the holes on the bracket with the holes on the wall. Drive one long bolt through each hole to secure the bracket to the wall.
Place the new microwave template on the bottom of the wall cabinet. Determine if the holes from the previously installed microwave match up to the holes for the new microwave template. If they do not, drive a hole through each noted location on the template.
Lift the microwave onto the wall bracket and hook it on to the bracket with the slots on the rear of the microwave. Lift the electrical cable up through the hole in the base of the cabinet where the previous microwave's electrical plug was inserted. Drive one bolt through the top of the microwave to attach it to the cabinet at each hole location.