Setting up a lock on your device will help keep your information secure. A screen lock will prevent others from getting into your device unless they have the necessary credentials. If your device is requesting a PUK code, you need to contact your carrier to unlock your device. Removing your security lock will allow anyone to be able to unlock your device.
From the Home screen, tap Apps.
Scroll to Lock screen and security.
Tap Lock screen and security.
Tap Screen lock type.
Select a screen lock type. If necessary, follow the onscreen prompts to complete setting up a screen lock.