1. Remove the five screws located on the back of the PS3 controller. Set them aside in a place you won't lose them or accidentally knock them over while you're working on the controller.
2. Turn the controller upside down with the bottom of the handles facing you. Position your hands so that each thumb is pressing into the center of the controller between the two handles on the side facing you, not the top of the controller. You'll notice a thin line running around the controller where the top and bottom pieces are joined. Place your thumbs so that one is under the line, on the bottom half of the controller, and the other is above the line on the top half of the controller.
3. Press inward with your thumbs while pulling the pieces away from each other. A clip is located inside and holds the two pieces together. You might need to apply a lot of force before the controller pops open. If you cannot get the controller open using your hands, insert a small, flat piece of metal into the slit between the two pieces and push upward until the controller pops open.
4. Reassemble the controller by snapping the two pieces back together again and replacing the screws back into the holes. Make sure the screws are tight. If the controller won't work, try taking it apart again. Make sure everything lines up properly when snapping the controller back together.