Unplug the microwave or shut off the power from the circuit breaker box if you have a built-in unit.
Open the door and use the end of a flat-head screwdriver to pry off the inside panel. Support the handle with one hand while using the other hand to remove the screws on the inside of the door. Pull the handle away from the door and discard it.
Hold the new handle against the door so the screw holes match. Insert and tighten the retaining screws to secure the handle.
Close the door and plug the microwave back in or restore power from the circuit breaker box.