Just started to fit my new blue belts to my 2005 G cabriolet but been having a few problems and could do with some help asap!

For the rears I have taken out the bottom part of the seat but how do you take out the back part?
I been searching for bolts holding it in, I got the bottom part free but its stuck at the top and making it really awkward to get to.

Also I managed to take the cover part off which covers the seatbelt mechanisms but what size bolts are holding the mechanisms in place? I think its about 21mm but thought I'd confirm first as I dont wanna mess anything up.

Thanks for any help.