Not to be an ass, but search, I know there has been many topics on this.
First yes, take them off. You dont need to go crazy and spend 20 hours sanding, unless, you have some nasty curb rash.
Clean them, degreaser, soap, what ever.. get them clean. Then get a brillo pad, and some 200+ grit sand paper. go over all of the wheel.
Next, get some tape and newspaper, cover the tire. Then spray, Id say do about 3-4 light layers. If you do to heavy you will get runs and such. Then do about 2-3 clear coats.
Heres a pic of mine, took about a day.. just cause the dryin time.
I have had mine painted for over a year now, and prolly need to do it again, cause the salt from winter killed them, but im gunna wait until spring.