Will be best to take the bumpers off first mate. You can just spray the sides while on the car.
- Sand down with loads of different grades, starting with a rough grade then working down to smoother one (about 1200 grade).
- Apply primer (3 or 4 coats), leave a good hour ot 2 inbetween coats.
- Leave for a couple of days for the primer to dry, then lightly sand with 1200 grade paper to get it realy smooth.
- Apply 4 or 5 coats of posi blue, again leaving an hour or 2 between boats, and leave it a couple of days to dry out.
- Lightly sand down and then apply 4 or 5 coats of lacquer, leaving 1 or 2 hours between coats. Leave for a few days to harden, then refit the bumpers.
This is a very tricky job to do and should only be attempted if you know what you are doing and have all the right gear. Otherwise, take it to a bodyshop.
This is only a very rough guide, but it gives you an idea mate. Hope that helps.