Unplug the DeWalt sander from the electrical outlet. Flip the sander on its side or casing to expose the Velcro pad.
Locate the screw fastener, or fasteners; DeWalt sanders feature either one or three screws that secure the Velcro pad into place. Insert the correct size Allen wrench into the head of each machine screw and turn the screws counterclockwise to loosen and remove.
Slide the Velcro pad off the sander and insert the replacement pad onto the tool. Align the pad's holes with the sander's holes.
Apply a thin layer of medium-duty thread lock to the machine screw threads. Rethread the screws to secure the new Velcro pad onto the DeWalt sander.
Tighten the machine screws with an Allen wrench.