Windows can dress up the appearance of what's often a pretty bland portion of your home--the garage door. If you want to add windows to an existing garage door, you may be in luck. Garage doors are constructed of panels, which can be replaced individually. If you can find a replacement panel with windows from your door's manufacturer, you're ready to go. You'll only need a bit of time and some simple tools.
Raise the door to it's upright position. If your door has an electric motor, unplug the motor. Place a ladder under the right track, at the back end. You'll see a hook for the end of the spring on that side of the door. The spring's tension will be off of it, so it will be easy to unhook. Unhook the spring from the other side in the same manner.
Lower the door. Be careful--without the springs, the door will be heavy. Place the door all the way in the down position.
Remove the bolts holding the track wheel assemblies and the hinges connecting the door panel to the surrounding panels. Remove the hardware.
Enlist an assistant to help you. Position one person at each end of the panel you'll be removing and grasp the top edge of the panel. Tilt the panel back slightly, so that the top edge of the panel is clear of the lower edge of the panel above it. Pull the panel steadily upwards, sliding it clear of the tracks for the door. When the panel is completely separated from the rest of the panels, set it aside.
Lift the new panel with windows up and position the lower edge of the panel parallel to and slightly behind the panel above. Carefully and evenly slide the panel downwards until it is position between the upper and lower panel.
Place the hinge hardware in position, matching the holes in the hinges with the pre-drilled bolt holes of the new panel. Slide the hinge bolts into the openings and tighten with your socket set. Insert the wheels of each of the track rollers into the tracks and position the mounts for the rollers in place over the holes in the door. Insert the bolts and tighten them to hold the rollers.
Lift the door back up to the upright position and replace the springs. Plug the door motor back in if you have one.