Changing your Lock Screen PIN or Password
From the Home screen, tap the Apps Key
> Settings 
> Lock screen.Tap Select screen lock.
Enter your current unlock sequence, then tap Next.
Tap PIN to change your number lock sequence or tap Password to change your alphanumeric lock sequence.
You’re prompted to enter and reenter your new lock sequence.
From then on, you will need to enter that sequence and tap OK to unlock the screen.
NOTE
You have 5 opportunities to enter your unlock PIN or password. If you used all of the opportunities, you can try again after 30 seconds.
If you have set up a Microsoft Exchange account, you might only be able to use a password for your screen lock.