Alright, if no one else will tell him, I guess since I'm probably younger and dumber than this feller, it's safe to say I'm not "helping him be young and dumb".....
Lock the bolt open on the bolt stop before doing anything.

Behind the trigger gaurd there is a rounded tab with a hole in it, press this forward and pull up out on the trigger guard, the trigger group will pop out and the box mag will come out at this point. Simply replace the trigger group and the detachable mags will pop in and out. You'll notice the body of your box mag has a large lump at the rear just below the mouth that locks it into the gun, detach mags don't have this.

If you've got a wooden stock on yours, you'll likely need to do some sanding on your mag well in order to make the detach mags work well, on most of them I've had, the well is too small and pinches the mags (if you can get them in at all) to the point that the follower stops at about three rounds and you jam up.

Mind you, mag capacities over 5rnds are illegal for hunting, not that the original mag IS legal, but moreso than a 30rnd detachable magazine.