Very carefully or you will catch a Spring to the face.
On the back of the mag you will see a metal L shap floorplate just sticking out behind the plastic for plate. Take a flat blade screwdriver and pull it toward you until you hear click. Then carefully slide the floor plate off. Keep it pointed away from you or the Spring will get you.
Thanks Case, I managed to open one of my old mags, but I got 2 brand new and I a bit struggle, but maybe its just tight. New mags are much quitere than old (when I press red plastic old ones do a laud click)
I talked to SAI ,EU & USA About putting out a FYI About them . I had one get me . I think I did a FB video on it . I will add it to my list of upcoming videos . Now that there are more A2MF out and people are getting them .
I did a write up on the mags of Which models use which and forward/ backwards compatible of them.