Hey while its not overly difficult, its also not really obvious how to replace your fixed stock with the Hinge Assembly. I included some quick short instructions on my website where I list the AT-X Hinge Assembly for sale:
The AT-X Hinge Assembly is the part that converts the Accuracy International AT-X Rifle into a Folding version of the AT-X. The AT-X is designed to be either
www.bisontactical.com
Here they are as well (since I just replaced mine):
Below the manual calls for 44.3 inch pound torque settings for #4 (bolts to main chassis), and #5 which is the bolt to the rear chassis. These are basically the same bolt sets you will use for replacing the fixed chassis with the hinge assembly. The AT-X Hinge Assembly comes with (4) M6 hex screws and (1) M5 hex screw. You will need to remove the part below that is between the screws #4 and #5.
Additionally, you will need to remove the below part as well (between #1 and #2). You will then replace these with the Hinge Assembly.
edit - of course there are the other parts like the part that keeps the stock in the folded position - those are pretty obvious so I didn't include them...