Tools required...
1/ Hacking out knife (to remove the putty)
2/ Hammer
3/ Wallpaper scraper or similar (to ease glass out) and to remove glazing beads if beaded
4/ Putty knife
Materials...
1/ Replacement dgu's
2/ Bytul putty, do not use linseed if you want the new units to last more than a year, better still bed them on glazing silicone
3/ Panel pins
To measure....
Measure the opening and deduct 5mm of the width and height for the manufacture size
To fit...
Hack out putty using hacking out knife or use scraper to prize beads away if beaded, ease dgu outwards from inside with scraper, clean out remaining putty. Use new putty on rebates or clear silicone, push glass onto this and hold in place with pins if finishing with putty, otherwise replace beads using panel pins to secure.
Cost....
Small units are quite cheap, bigger ones are more expensive