I'd avoid doing this.
Basically, you do a light (typically wet) sanding by hand (very carefully), prime it with an appropriate primer (maybe a few times) and then paint over it with an appropriate color. However, since the sanding has to be done carefully (since its easy to destroy carbon fiber by sanding), you're going to end up paying someone a lot of money to do this (since it takes a lot of time to prep the frame).
You can't really use chemical strippers or other techniques that you'd apply for aluminum and steel frames can destroy the carbon fiber. You also can't do things like powder coating for the paint step, since you have to heat the frame to the point where the carbon fiber can be destroyed.
If you're really insistent on doing this, there are shops which specialize in repainting carbon fiber. But, they'll charge you an arm and a leg due to the amount of labor they'll have to put in to prep the frame for repainting.