Garage Door locks often need replacing due to wear and tear. If you want to save some money and not pay a professional, read this post on how to remove the original lock.
Before you start, secure the garage door down with vice grips. After this is done, remove the pin which secures the inside of the lock handle to the lock shaft. You can do this by placing a nail over the pin and then tapping the nail with a hammer, until the pin is exposed.
You have to now pull the inside handle off the shaft and pull the lock bars off. The lock bars are two straight pieces. Then disconnect the deadbolt lock, by removing the four screws with a screwdriver. After the deadbolt lock is removed, unscrew the screws that secure the outside lock.