Its easy really.
1- Remove top cover and bolt tray. Don't lose those tiny screws.
2- Remove stock, two screws in the top and two underneath.
3- Remove pistol grip with the single screw underneath.
4- Remove front end by taking out the two screws in the mag well and the two in front of that. Then just slide the entire assembly forwards and off.
5- Remove fire select lever. The button covering it should have a place where you can pry it off. Take out the screw underneath and keep all the washers in order and right side up.
From this point it should be a simple matter of lifting out the mechbox and replacing it in your new body. Then put it all back together again and bingbangboom.
Edit: Dang, beat me by one minute lol but I did it from the top of my head