Here is the lock in question for others wondering which one it is:
http://www.padlockdistributors.com/master-lock---1630---suitable-for-lockers-with-gravity-lift-handles_656prod.htmlThe lock will require the key in order to change the combination.
How does it work? Check out the patent and drawings; they can give you more clues.
http://www.google.com/patents/about?id=Y_NRAAAAEBAJ&dq=3031877Remember, if this is not your lock, only a locker you were issued at school or university, please follow the rules of locksport (hobby lockpicking) and do not mess with it, do not pick it, and do not take it apart.
If it is your lock and it isn't attached to a locker, you should be able to take it apart and figure it out, or you may have to drill some rivets out in order to get inside.
Good Luck
Squelchtone