They are pretty simple really.Do one at a time so you have a reference. If you decide to go after both at the same time, don't mix the parts from carb to carb. Keep everything organized, and be very careful when you remove the diaphragms from the tops of the carbs. They can easily rip.
Here is a guide. I would read it first. It is a lot to read, and they list the specs for the float height as well.
Pull all jets and clean with carb cleaner. Use air to blow out all passage ways and make sure your cleaner gets in all passage ways. Clean everything as best as you can, especially any varnish on the needles and anywhere else.
Make sure your float valves are clean and work, also polish up the float valve seat with some fine steel wool before closing up the carbs. Take the seat completely out. Don't leave them in the carb body. There is a passage way under it which needs to be clean and clear. If there is any debris in this passage way, or under the seat, the float valves won't work and you will be flooding the carbs with fuel/overflowing.
Depending on the year of the carbs, you either have brass floats or plastic. If brass, make sure they float and no cracks. You can shake them to hear if there is fuel in them. Another test is to submerge in hot water and look for bubbles.
Be very careful with the floats. You do not want to twist them or your fuel levels will be off. If gaskets are dry, replace them.
After they are put back together, you will have to sync the carbs. You can do so via a simple home made monometer. http://www.xs650.com/forum/showthread.php?t=2317
Some clear tubing, divide it so it is equal in length on both sides, get something to attach it to (pole, yard stick, broom stick, etc.) and I use Marvel Mystery oil for the fluid. It is red and won't hurt the engine if you get a little sucked into the carbs. However, have your finger on the kill switch when starting the bike with the monometer attached. If one carb pulls fluid, it will be quick. You don't want to hydro lock the engine. A little fluid won't hurt. But you don't want to suck it all in the engine.
You will find that very small turns of the center sync screw is all that is needed to get the fluid moving in the lines. Turn it until you get both sides equal in the lines.
Almost forgot. Most importantly: Set cam chain tension, adjust the valve lash, time it, and then carb sync... In that order.
If you don't have the others to spec, you will be chasing problems with the carbs and you will get nowhere.
99% of the time you do not need a rebuild kit for the carbs. Maybe gasket(s) and that is it. Try to reuse the stock parts. Many aftermarket parts are junk.