Verified answer

You can't, even on resettable padlocks you must have the existing combination to reset it.

If it is one you set your own combination on I have no suggestions. If it is a Master brand dial combination padlock and has a serial number on the back take it to a locksmith and they can probably look up the combination for you. If it was provided by the school and has a key override on the back you will have to talk to someone at your school.