First, the screws are M5. An 11/32 wrench will do just fine. The plastic fasteners holding the trunk liner come off real easy (the top four with a flat screwdriver, the bottom four with a plier). It's helpful to have a partner to put the nuts back on the screws while you push the spring back. When putting back the plastic fasteners, separate the two parts and insert the bottom part first.
It's really ridiculous that a job that should take 15 min. took an hour because I had to make a trip to the hardware store to buy a dremel tool since BMW does have replacement parts that don't fit properly.
My next one won't take more than 20 min. + $68 for the part.
Bottom side. The ridge needs to be filed:
Top side. You need to cut out as shown: