Swipe down from the top of the screen to reveal the Notifications menu.
Tap the Settings icon.
Under My device, tap Lock screen.
Tap Screen lock.
Tap the desired security setting. Note: For this demonstration, tap 'PIN'. See "Set Pattern Lock" article for more information on the Pattern option.
Enter the desired PIN, then tap Continue.
Re-enter the desired PIN, then tap OK.
If you have forgotten your pin or password screen lock, a master reset is required.
Learn about the importance of adding a password on your device to protect your privacy as well as how to report a lost or stolen phone here: www.att.com/stolenphone.