How do I remove the rear seats?!

Hi guys (I'm new!), I was wondering if you could help me - yesterday I bought a leather interior for my Audi A6 Avant (1999) and tried to fit it today. Front seats were easy, logical and straight forward removal and refitting. The back seats however have presented much more of a challenge - I got the base bit (the bit your bum sits on) off no problem, it just lifted straight out, but I can see how the bit your back rests against comes out. Being the Avant, its a fold down 40/60 split seat. I've put the seats down and the only things I can see are bolts which look like you cant undo them unless the seat is already out (as otherwise it would be in the way).

Any help you can give would be much appreciated! Thanks :)