Are you referring to the four strokes? I've done it on those. They don't generate a lot of power at idle, but are OK when up higher in the RPMs. It's pretty easy, you just have to pull the flywheel, so getting the flywheel nut off and using a puller on the flywheel is about the hardest part. To get to the flywheel you also have to pull off the pull-start assembly, but that's only three 10mm bolts.
You have to know which version you have. The older models (I think -A2 and before) only have one coil inside for the alternator, but I believe the newer ones have two. I don't think it changes the output though, as they are both rated for 60W (roughly 5A)
Depending on what you want to use it for, you may need a rectifier. If just used for incandescent lighting, you don't, but for LED lighting or charging the battery, you'd want/need the rectifier.
I've been playing around recently with mine and just added a full-wave rectifier to it. The stock one is just a diode, so you lose 50% of the output turning it to D.C. with just a diode. A full-wave rectifier allows the use of all the output but it does add a bit of voltage drop (about 0.7V). I've also just started to put a DC-to-DC converter so at low RPMs it would develop more voltage but I haven't tested the total output yet.