First rub it down with "wet & Dry" 320 sand paper (by hand) and youll also need a bucket with warm water and a bit of fairy, to use it with.
After the previous paint is in a dry and matt condition you can start primering. TRY to stay away from aerosols as they're too thin and run easily.
See if you can get to a mates bodyshop and "borrow" his air gun.
Lay the primer sparingley and evenly so you dont get a single run!
Give it another coat once its dry. (primer basically builds up and gives the new paint more contrast)
Now you can paint using the same technique, any colour you wish!!!!!
Good Luck.
As for fitting i see two screw's in that pic. Place it against the boot pull out the screws, line it up sqaure then put a marker through the holes and make a point on each side. Now you have your drill points!!!