Changing Your Screen Lock
Tap the Home Button
> touch and hold the Recent Apps Button 
> Lock screen settings.Tap Select screen lock.
Confirm your unlock information (if necessary).
Tap the desired screen lock option.
You’re prompted to enter your screen unlock sequence (and Backup PIN, if necessary).
If you've set up a Microsoft Exchange account, you might only be able to use a password.
After 5 unsuccessful attempts to unlock your phone, you're prompted to enter a text phrase to confirm that you're trying to unlock your phone, unless you've set a Knock Code. After 6 unsuccessful Knock Code attempts, you're prompted to enter your Backup PIN to unlock your phone. If you've set a Knock Code, after 6 unsuccessful attempts, you're prompted to enter your Backup PIN to unlock your phone.
You have 10 opportunities to enter your unlock sequence. After 10 unsuccessful attempts, your phone will automatically perform a factory data reset and all of your personal files will be erased. You will be warned after the 9th unsuccessful attempt.