One side of the window will have beads which pop off with the help of a couple of filling knives,the other side will have a wedge gasket(rubber seal) or security tape.
I'm guessing u will have wedge gasket if so remove this first prying out gently with a flat screwdriver works for me then the unit will be loose,nows the time to pop the beads off and carefully remove your unit.Refitting is the opposite using a clean peice of wood maybe to tap the wedge gasket back in last off all.
If security tape is used its normally on the inside and you will see it between the unit and frame normally 2-3 mm thick post back if you have this and i will try to help out (its almost as simple).
following on from sashwizard, if they are gasket type, it helps to lubricate the gaskets before re-installing, as this is how they would have been when new. oh, don't forget which way round the gasket goes as both sides are similar but not the same.
You will have to take out the old unit to get the correct size
Height X width X thickness, any glass above 800mm from floor level must be toughened.
JonB
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