You can do it on the side or centre stand. Just do 1 fork leg at a time. Loosen the Tripple clamp bolts, so they are just still holding tension, and slide 1 fork leg up. If it doesn't want to slide, loosen the bolts a little more. Once it is moving through, find something to measure it with, when you are happy (5 or 10mm is all you need) lock up those bolts again. They don't have to be super tight, but you don't want them falling out! Now do the same for the other side. Simple!