Use a light amount of force when removing the screen.

A black ribbon cable attaching the display to the motherboard and a black cable attaching the home button to the motherboard will be damaged if you force the screen off.

Starting at the top of the device, work the plastic opening tool under the screen. The top of the device has the Samsung logo and headphone port.

Start separating the screen from the glue. Work your way around the screen until the glue is no longer holding the screen in place.

The screen will not come off completely yet, there are still cables attaching it to the phone.