How can I replace a wheel arch moulding?

[Spanky Deluxe]

At the beginning of the year whilst on a skiing holiday we came back to find the rear left door handle and wheel arch scraped up - apparently someone else's car had slid and struck our parked car and they decided to drive off. Most of the damage to the handle was transfer and there's a small paint scratch where the metalwork meets the wheel arch but nothing too serious. The most noticeable part though is that the wheel arch plastic is completely scratched up.

I've got a replacement wheel arch from eBay (that alas is still scuffed a bit but nowhere near as bad) but can anyone suggest how I can fit it? I've had a look at the car and I've got no idea how I could go about it. There are five holes through which it's held on but I can't see any obvious way of undoing them on the car.