Depends on the pipes feeding your radiators - if there is additional "give" on those, you might be able to raise it, but could put pressure on the pipes running underground, might be lucky / unlucky with this - it's something I wouldn't recommend...
If you do go down that road, then you need to take off each radiator & raise the rad bracket, it's not a difficult job if you have done something like it before... you can either drain your heating system (assuming you are able to do this) then take off the rads, or drain each radiator individually... it can be a messy job.
Would it not be easier to cut the skirting to fit the rads. Are you planning on fitting the skirting yourself?