headnote: make sure you take note of which pattern (36 spoke 4 cross, 3 cross, etc.) you have, or make a diagram of the pattern so you lace it back up right again. I had to undo a lot of my lacing to change patterns=pain in the neck
1.) Remove tire and tube from rim (use a tire lever to pry the first tire wall out of the rim, then move around the rim until it is fully loose, then pull out the tube and remove the tire the rest of the way).
2.) Using a screwdriver (on the outside) or spoke key/wrench (on the inside), loosen all the nipples--small metal pieces holding the spokes to the rim--and as you do this, unlace/untwist the spokes and slide them out of the hub.
3.) You should now have all your spokes in a pile and all the nipples in another pile (a small cup w/ lid is recommended so they don't go wandering away), and your rim and hub sitting by themselves. Thoroughly clean all parts (use water or solvents but make sure they are not harmful to the parts, and be careful with the hub interior parts) and dry them.
3.1) (Optional) If you are going to paint the spokes or any other part, do it now, but I would advise against painting any of the following: spoke threads, hub (so you don't interfere with its ability to function properly), braking surface of rim (I just masked this with short strips of scotch tape and it turned out OK, not great, but OK, if you paint it, your brakes will probably get really gummed up and not work too well), nipples (they look better as metal color plus could get messed up by paint pretty easily). To get a really good look, sand, prime, and multi-coat all painted surfaces and add a clearcoat for protection if you want it to last for a good long time (I did none of this and will probably have crap in not too long, but I'm ok with that).
4.) Reassemble. This step is fairly complicated but there are many good tutorials on youtube that will walk you through the process. The one made by biketube was the one I used and it was great until I found out that my spokes were made to be laced 4 cross and the video was for a 3 cross setup (each spokes will either cross 3 or 4 other spokes most likely, possibly less). You basically do it in four series, first the spokes on the left side (arbitrary which side that is) going in one direction, either clockwise or counterclockwise from the hub. Then the right side going in the same direction (CW or CCW) viewed from the side, as in, when you look at the wheel from the side all the spokes are either going out from the hub in a CW direction or they are all going in a CCW direction. then you pick a side and start going in the conflicting direction to the ones you already have in, and vise versa for the last series. There is a lot more to it, so watch the video or find a detailed tutorial.
5.) Tension, true, get back on the road. Enjoy your newly built/rebuilt/repainted wheel!