Unusual to find a single glazed uPVC! Anyway, the glass pane is held in by the plastic glazing beads that could be either inside or outside. You need to carefully prise these away with a chisel or similar, and once you have them all out the glass can be shifted. The glass may be secured with a sticky both sides foam tape that has to be slit before the pane will come free. Careful with those glass beads now - they can be very difficult to shift if they've been in a while.
John, May 2009
