Hi, I have done this.
Bascally you will need to cut open & remove the rubber lugs under the sills (6 in total, per side IIRC).
With these removed you will see bare metal around the holes in the bodywork, purchase some underbody seal & give it a good coating - otherwise you will regret it when your car rusts away.
The jacking 'domes' underneath stay put, place the skirt around them - DONT remove them as its a knightmare to fit back.
Remove the side circle discs though.