when I fitted both of mine I had to drill the head off the bolts as they were torx bolts and rusted to fuck, once the heads have been drilled off you can lift the old spoiler off and then get to work on whats left

you will need to drill 2(1 each side) new holes in front of the ones on the outside edge, the middle ones are fine
will need to remove the old riv-nuts
and drill right the way through so you do the bolts up as shown in the pic below
think thats about it
if you want any more info just shout matey