Replacing the oil in a fork is very easy.
Replacing the seals requires some attention to detail, but isn't technically difficult.
However, replacing the OEM spring with a heavier spring requires cunning, tenacity, creativity, and patience. 
This isn't a tutorial, the manual is good for that; instead, here are some tips on how to git'r done easier: - Before you remove the forks, measure from the top down to the triple clamp. Don't rely on marks from a permanent marker. You should, however, mark your handle bars before remove those.
- The problem with a heavier spring is it's thicker than the OEM spring (6), and will get stuck on the plastic piece in the middle of the damper rod (7). To fix this, clip the outer cup away, but leave the spacer and as much of the arms that connect the cup. (I didn't get a photo of this, but if someone has one then please send it to me and I'll post it here).
- The other problem is the new spring sleeve, which comes with the set of new springs that you get from RaceTech, is too thick on the inside. It's aluminum instead of the OEM steel, so you're better off just cutting the OEM steel spring sleeve (5) to size. We cut 17mm (the difference between the two springs) off of the end that doesn't have the plastic piece (yellow) on it. In the diagram (above) it makes you think that the little plastic piece comes off easily, but in fact they're fused together. You'll actually cut through the holes, but it'll be okay. You need to have a pipe jig in a clamp to get a straight, right-angle cut. (see image below)
- To make life easy when reassembling everything, put in the spring sleeve first, then the spring. That way you can reach the damper rod through the spring (because it'll be down in there -- be sure to put the lock nut on the damper rod before putting the spring in). Reach in with needle nose pliers, spin the spring to "thread" it up, and then (with the help of a friend) use flat screw drivers to inch the lock nut up until you can fit the washer (not in the diagram, but needed on each side of the spring) and the slider (which is the c-shaped washer that slides in).
- To further make life easier, keep at least one old oil seal, slice it in half, and then use that to pound in the new oil seal. Seals are made out of steal, so you'll need a good cutting tool, like a Dremel disc to cut through smoothly. Don't just cut one end and then bend it around the fork, it'll never bend back into shape. Instead, cut the circle into two c-shape pieces. It will also be a good idea to slice off a layer of the inner rubber. Then, using a rubber mallet, hammer that nice new seal into place using the old seal as an in-between.
In addition to tools ... 1) Get a good manual, like Haynes 3290.
2) Get a good friend, maybe someone smarter than you and with better tools than yours.
