Just to add to this (I just had to remove mine):
1)There should be a Phillips screw on each end of both sideskirts
2) There will be plastic plugs alone the underside of both sideskirts
3) The plastic plugs have two parts: an outer sleeve which is the plug and an inner plastic screw. The inner plastic screen needs to be removed first to properly remove the plastic plug. The plastic inner screws have a Phillips head and often are so delicate that they will strip out and not come out when turning them left. To help get them out, pry the two part plug out slightly with a flat screwdriver, then attempt to pry out only the inner screw, it should come straight out without much force (assuming you can get the screwdriver under its head)
4)Once the end screws and plastic plugs are out, the sideskirts should easily lift up and away from the car (sliding out of the metal guides which the tabs of the sideskirt fit into).
These sideskirts fill up on both ends with sand and road dirt very easily and should be cleaned out occasionally to reduce weight (about a total of 10 pounds of wet sand for me) and help reduce strain on the sideskirts. The weight (as in my case) will begin to warp and crack the sideskirt.