take off ur rims, buy paint stripper to strip off the existing paint (buy some scotch-brite pads to help "sand" away the paint)...
after the paint is gone and it's bare metal, you can apply your first layers of primer....usually 1-2 coats of primer is good...let it dry
once it's dry and looks smooth (if it's rough, u might wanna sand down with really fine sand paper/scotch-brite pads) u can start applying your colored paint. 2-3 coats of color, followed by 2 coats of clear.
This process will take you a few days and leave your car wheel-less. You can do it 1 wheel at a time while using ur spare....
you do not need to take off your tires either...go to your local casino (if ur underage, tell ur older brother or dad to go for u) and grab a few decks of used playing cards. Wedge the cards around the outter edge of your rim (between the tire and the rim) and spread them out with them all standing up
like so...
grab about 4-5 decks...
if you have any further questions, google if your friend, there's TONNES of DIY threads from other forums showing people how to paint your own wheels...
Good luck!