How to Replace Polycarbonate Windows on a Garage Door

Lower the garage door. Slip the head of a standard screwdriver between the trim and the door's surface in any location along the trim. Pry the trim off the frame of the broken garage door window from inside the garage with the screwdriver. Remove the frame from the garage door, it is held in by the trim and will be completely free. Remove the broken polycarbonate panel. Take out any inserts that may be lining the opening of the garage door -- some doors have removable inserts in order to create different window shapes.

Take the polycarbonate panel to a home improvement center or glass shop. Alternatively, measure the empty hole in the garage door, measuring from top to bottom as well as from side to side if the polycarbonate was completely shattered. Have a new piece cut to replace the piece you've removed. Place the frame upside down on a soft surface once you've returned home. Lay in any inserts first, followed by the new piece of polycarbonate.

Insert the frame into the opening in the garage door, from the interior, with a friend standing outside. Instruct your friend to hold the frame and polycarbonate panel upright inside the garage door window's opening. Reinstall the trim by pressing it into the door, with your friend holding the framed polycarbonate in place. Tap it gently with a rubber mallet if the trim will not seat easily.