Disconnect the power cord from the electrical outlet.
Peel off the sanding disk from the sanding pad on the bottom of the sander.
Loosen the mounting screws through the holes in the bottom of the sanding pad with a Phillips screwdriver or an Allen wrench (depending on the type of screws on your sander). Lift off the old sanding pad.
Position the new sanding pad onto the bottom of the sander, and fasten it to the sander by tightening the screws through the holes in the pad.
Place a new sanding disk on the sanding pad. Plug the sander into the electrical outlet, then turn on the sander and begin sanding.