Removing a double glazed window can be quite labour intensive. If you decide to try it yourself, make sure you give yourself plenty of time, and wear gloves and goggles.
Begin by unscrewing all opening windows at the hinges and removing them. Then take away the beading and putty around any fixed panes and take them out too.
Once you’ve removed all the glass, use a saw to put angled cuts in the frame, and a bar and hammer to remove it in sections. You should remove the sill if you’re going to replace that too.
Finally, cut through any screws holding the frame into place with a hacksaw.