It might be glued or nailed - most likely with a power nailer, with recessed heads filled so as not to be visible.
Either way, be prepared for it not to come off non-destructively. [I replaced all the skirting in my hallway when I fitted wooden flooring earlier this year].
Besides destroying the existing skirting, you will probaly damage the plaster in some places - so have some Pollyfilla ready.
When it comes to refitting the new skirting, GripFill works pretty well - but may need to be supplemented by the odd screw if the wall isn't straight.
When fitting my new skirting, I cut and mitred it and then painted it
*before* sticking it on the wall. There is then no danger of getting paint on the new flooring - and any slight gaps can be filled with a bead of decorators' filler, and the paint touched up if necessary.Besides removing the skirting, you will of course have to undercut the door frames and achitraves so that the flooring can be slid underneath.
HTH, Roger