I sucked the old oil out the top with a nifty little siphon-pump I had laying around the shop. Others have reported using turkey basters with some success. In any case, I did it to refresh the oil since I was working on a used bike and wanted a good baseline for my own information. Once caveat, removing the oil is a whole lot easier if you pull both springs and collapse the forks bringing the oil and the bottom of the fork to its highest point.
On the other hand, I helped a friend install Progressives in his forks and we just pulled one spring at a time, allowing the oil to drain back into the tube and then replacing with the new spring. Didn't even jack the bike up and it was easy enough.
One thing, if you lay the old spring and spacer on the garage floor and lay the new spring next to it you can judge whether the pre-load spacer is going to work or if you have to cut a new one form the supplied PVC. A lot easier than mucking with it after the fact...
