Ok this problem has been answered many times in this forum so must be a common fault.
I will try to keep it simple by using pics of how I did it, here goes.
This is the problem, seatback only open a little then stops.
You will need a T30 Torx bit to undo the bolts (one either side).
I have shown the bolts with the seat back down, on refitting for clarity (you have to undo them with the seatback pulled out as far as you can)
Lift the assembly out and you will see a wire (blue arrow) leading to a spring strip (red arrow) just under the point of the red arrow, at the end of the strip is a small stud that runs through the steel support, this is the culprit, pull the strip towards the centre of the armrest and the support will be free.
Apply a small amount of grease to the stud and the problem should not arise again.
Hope this helps, GeorgeM.