WHAT are you talking about???
The lower receiver doesn't have a "HANDLE". The upper receiver has a carry handle and it's either permanently fixed or it's removable with 2 thumbscrews on the side.
If you are talking about the GRIP, then you insert a 3/16" allen wrench up the grip and loosen the screw. (BTW - Rock River Arms uses an allen as well)
If you are talking about the BUTTSTOCK, then it's the big screw at the back, on the top.