Many garages will have a service door on either the side or the back. This door is generally able to be locked so that the items in the garage are safe and secure. If something happens to damage this lock, it will need to be replaced or people will be able to enter your garage whenever they please. Replacing an exterior lock is not any different than replacing an interior lock. The difference is the knob itself, as it is more sturdy because it has a key lock instead of a push button or turn knob lock
Use a screwdriver to remove the two screws securing the doorknob to the door. These screws should be located on the inside side of the door. Pull the two knobs apart and away from the door.
Remove the two screws holding the strike plate to the door jamb. Pull the strike plate off of the door jamb and slide the bolt, the portion which holds the door closed, out.
Slide the bolt for the new doorknob into place. Make sure that the flat edge of the bolt's tongue is facing the inside side of the door and the curved edge is facing out. Place the strike plate over the tongue and secure both the bolt and strike plate with screws.
Insert the knob with the key hole, through the hole in the door. Make sure that the stem on the knob fits through the hole on the inner portion of the bolt.
Place the mounting plate over the stem of the exterior knob, on the interior side of the door. Push it on until it is flush with the door. Put the interior door knob over the mounting plate. The stem should fit into the hole on the back of the interior knob. Push the knobs together until both are flush with the door.
Insert two screws through the holes on the front of the interior doorknob. Tighten these screws to hold the door knob to the door. Close the door. Test that the door is able to close securely and lock and unlock easily with the supplied key.