You should consider at one additional 15 or 20 amp circuit. Is your garage a wet environment? A Ground Fault Interrupter (GFI) breaker might be useful.
If your main fuse panel is in the garage, it should be quite straightforward.
However, I STRONGLY recommend the skills of a licensed electrician to do the work! You may only be allowed one mistake!
BTW, if your garage is typical, that lighting could stand some improvement, also.
Jim