Unplug the microwave's electrical cord from the wall outlet.
Open the door of the microwave. Use a flat-head screwdriver to pry off the plastic cover on the inside of the door. Be very careful not to damage the cover in any way. Take your time when you pry off the cover.
Locate the two screws that hold on the handle. Use a Phillips-head screwdriver to remove the screws and take off the handle.
Place the new handle on the microwave so that the holes in the handle align with the holes in the door. Insert the screws from the inside, first by hand, then tighten them with the Phillips-head screwdriver.
Snap the plastic cover back onto the inside of the door. Plug the electrical cord into the wall outlet.