The roll covers are tightly fitted but with caution and a little tugging they will come off. I wore latex gloves and pulled. The covers have a little plastic ball that fits into a socket which makes them fit snug. After the covers are removed, carefully mark the holes and drill. You can get screws from a hardware store if they were not included. The brackets can attach to the plastic roll bar inside cover (black) as there are wholes already drilled into these from the factory. If you need any further info just drop me an email, I did this proceduce on my 09 Black Z4. I also have an extrta set of roll covers and another set of brackets for sale on eBay - cheap in case you make a mistake. New covers with wholes already drilled are approximately $33 each. Brackets for the windscreen are $19 from Germany.
It is really a simple task but take time and you will have no issues with the results