Go outside and locate the household service panel; this is a fairly large gray metal box mounted a couple of feet above ground with a small red indicator light on the door.
Undo the catch and open the door. Find the square recess in the center of the box covered by a lid with a sturdy half-round wire handle; this is the main fuse holder.
Grasp the handle and pull the cover straight out; the inside of the removable cover contains two thick tubular fuses held to flat copper prongs on either end by wide semi-circular copper clips.
Examine both fuses; you will immediately identify the faulty fuse by its charred appearance. To be on the safe side, unclip both fuses and insert two identical replacements into the clips; these fuses are usually rated at 40 amps.
Line the copper prongs up with their matching slots. Insert the fuse holder back into the recess and push it firmly home. Close the service panel door and secure the catch to complete the installation.