Only replace
WARNING: This page is about a different car, the 2011 BMW 750xi, 2011 BMW 750Lxi, 2010 BMW 750xi, and 2010 BMW 750Lxi. However, it is still accessible from the selected car via links, so may be relevant.
Have U-shape knife with 24 mm and 36 mm blade lengths (sourcing reference: BMW Parts Department) ready.
Fit respective knife with required blade length:
24 mm = All round on rear window
36 mm = Recut window edges at bottom left and right
Regrind blade with a grinding stone while machine is running (new blades also).
Insert knife carefully between tailgate and rear window.
Guide web of knife parallel to rear window.
Cut through adhesive bead as closely as possible to rear window.
Lift out rear window.
Pull off adhesive tapes all round.