1. To lock your device screen, press the Power/Lock key.
   
2. To unlock your device screen, press the Power/Lock key.
   
3. To set security lock type, swipe down from the top of the screen and tap the Settings icon.
   
4. Scroll to and tap Lock screen.
   
5. Tap Screen lock.
   
6. Tap Desired screen lock type and follow prompts to complete set up.
   
7. To change security lock type, from Settings tap Lock screen. 
   
8. Tap Screen lock.
   
9. Confirm PIN by entering PIN and tap Continue.
   
10. Tap Desired screen lock type.
    
11. Enter new password/PIN and tap CONTINUE.
    
12. Confirm PIN/password. Tap OK.
    Note: To learn more about requesting a device unlock for your AT&T mobile device, visit www.att.com/deviceunlock. If your device is locked and is requesting a "PUK" code, click here for instructions on how to obtain your PUK or PUK2 code to unlock your SIM card.