you on about the quarter window in the door or the one in the car?
if its in the door its not that bad......
bob the door card off (remove screws and slot it upwards!), unbolt the frame off the door (4x45 torx bolts) (marking where the bolts and adjustment wedges were before unbolting them) unclip the wiring loom off the frame, send the motor/window reg fully down, unplug the window motor.
remove the frame from the door and put it somewhere you can work on it (lounge floor?) then remove the main window. remove the bar inbetween the quarter glass and where the main window was, the quarter glass will now come out.
when putting it together the marks you made (red touch up pen/brush is best) to the bolts and wedges are invaluable to get the adjustment and fit back where it was!
ive never changed the one thats in the car so can't comment on that....