quick question about window regulator

[JonbmwX5]

hi all, after reading all the posted i now know my window regulator has snapped and used the guide on here to take the door apart (brilliant thanks)

i fould a small piece of plastic in the bottom of the door and its off the window regulator see pic below (left hand side of pic)

just one problem...... i cant undo the nut in the bottom pic .....err it seem so tight and when i try it, it slips and if i keep trying it will wreck the nut head, i had a feel of the back and its pastic, do i undo it from the back? any advise i would be very gratefull, thanks