Unplug the power cord from the electrical outlet, or turn the power off at the circuit breaker box if the microwave is hard-wired to the kitchen circuit. Remove the grill at the top of the microwave by unsnapping it. On some models, the grill may have retaining screws that you must remove using a Phillips screwdriver.
Remove the control panel retaining screw using the Phillips screwdriver. Pull the control panel away from the microwave and label each of the wires with tape and a marker so that you know their proper positions for reassembly. Unplug the wires from the control panel by pulling them off the posts.
Remove the old fuse from the compartment that the control panel was covering by grasping it and pulling it out. Place a new fuse in the compartment and push it firmly into the holder until it snaps into place. Connect the wires to the control panel according to the labels.
Place the control panel on the microwave and install the retaining screw with the Phillips screwdriver. Install the grill on the microwave and snap it into place. If your microwave grill has retaining screws, install those and tighten them using a Phillips screwdriver. Plug the power cord in for the microwave or turn the power on at the breaker box and program the microwave according to manufacturer instructions.