Haven't done it but I hear there are several methods.
This is the only method I can recall from memory:
Put the bike up on a rear stand and triple tree stand.
Put a floor jack under the front tire.
Loosen the bolts clamping the triple tree to the forks.
Jack up front tire until desired amount of fork tubes is extending above the triple trees.
Measure how much is extending on both tubes and make sure it is even.
Tighten down bolts.
Take bike off stands.
The other method I've read involves getting a buddy to help you hold up the bike while you loosen the triple tree bolts just enough to "walk" the bike down the forks a little. I don't fully remember the procedure to do this without dropping the bike though.