Remove the screws on the side of the door that help hold the handle in place. There are eight hooks on the top and bottom and four hooks on the hinged part of the door that keep the front and back of the microwave door together.
Pry the first hook out of the hole and slide a butter knife, putty knife or plastic wedge in the space to keep from the hook going back into place. Do this with all the hooks.
Apply some pressure to the knives and the front of the door will come off. Remove the damaged handle and replace with the new one. Snap the front of the door back into place and tighten the screws on the side of the handle.