First you need to hook up a timing light. Then its as simple as temporarily removing the vacuum line that goes to the distributor, loosening the bolt that holds the distributor in place, and turning the distributor until you reach the desired timing. Then tighten the distributor back down and recheck to make sure the settings remain intact.
Reinstall the vacuum line and remove the timing light.
All this will be in vain if you do not have a timing light and know how to use it. I suggest finding a friend who has one and has some basic knowledge.