If you have a carbon-framed bike, painting your carbon bike is little different from painting a non-carbon bike, although you will have to be more careful with cleaning. Normally, you would need to sand the paint off a bike before painting, but this isn't possible with a carbon bike, so painting simply involves covering the previous color with the new.
Take the wheels and saddle off of your bike. You can also remove the handlebars if you are not painting these. Clean your bike using a damp rag and soap to remove all grease. Do not sand the bike, as this will seriously damage the carbon frame. When the bike is free from grease, dry it with a dry rag.
Paint a layer of primer onto the bike. Use a paint gun if you have one, or use spray paint cans which are available from a hardware store. Hold the paint gun or spray can 1 foot from the bike when spraying, for optimum coverage. Spray on a layer of primer and wait for it do dry. Spray a second layer on when the first is completely dry. Wait for the second layer to dry before touching up any uncovered areas. Wait for all the primer to dry before continuing.
Spray an undercoat layer onto the bike. Since most spray paints are slightly transparent, this layer will show through slightly, so choose a color such as silver or white which will improve the look of the final coat. Wait for this to dry.
Apply paint to the bicycle frame using a spray can or paint gun. Proceed slowly, covering all areas of the bike. Do this in natural, or at least good light, to avoid missing sections. When you have finished and the paint has dried, check to see if you need to touch up any areas. Paint a second coat all over if you do. This will make the color more vibrant.
Wait for the paint to dry and paint on a clear layer of protection. This forms a varnish on the bike frame, and will prevent weather damage. Wait for this to dry fully before reattaching the wheels and saddle.