The trick is with the floor plate. You will see an oblong circle on the bottom of the ranger plate. It has a picture of a bullet on it. Push down on that. You will have to press the little tab on the rear/side of the magazine at the same time in order to push down on the bullet button. Once you get that depressed, the plate slides off in the direction of the tab/rear of the magazine.
ETA: They are basically the same as the PMAG Ranger Plates. They just have the added tab that has to be pressed to slide it off. They do stick a little.