How much can I raise the handlebars on my 800cc? ANd how do I accomplish this?

They make bar risers and if you go too high and you throttle cable won't reach, they make a throttle extention kit.

It already has a bar riser but was wondering how to raise it?

If you already have snopro style handlebars with the block. You just need to get a bigger block.

I ran the 6.5" riser on my 02 Zr800CC and had no problems with cables reaching. *The importaint thing here is to MAKE SURE you cut the cable ties that hold the wires that run up to the warmers(hand & thumb) and kill switch and leave them loose. *If you dont, they do reach but you may end up having problems with the warmers over time because when you crank the handlebars it will pull very slightly on the connections of the particular wires that I mentioned.
-JPL