There are basically two methods to deal with the existing skirting when we lay the floor.
Method 1: Remove skirtings and install the new/old skirting back after laying the floor.
Method 2: Leave skirtings in place and cover the expansion gap by nailing a bead of quad to the skirting.
Method 2 is the easier way. When using method 1, we have remove the skirtings first, which are usually fixed to the wall by nails or glue. Some minor damages may be caused to skirtings and wall. Some touch-up paints have to be done after installation.