Roll seat back as far as it will go, raise feet to windscreen, bl**dy hard double foot kick. Rinse and repeat until happy.
If you can’t raise your feet to the windscreen, take off a seat headrest, hold one of the metal supports and hit the other as hard as you can close into a corner of the windscreen until it breaks (so the point of the support hits the glass) then push and shove the main part of the windscreen out.