If using Microsoft® Exchange / Corporate sync, some screen lock options (e.g., face unlock, pattern, PIN) may be unavailable.
These steps can also be utilized to change your current screen lock setting.
From a Home screen, tap Apps (at the bottom).
From the Apps tab, tap Settings.
Tap Lock screen.
Tap Screen lock.
If presented with 'This device does not have a Google account associated with it...', tap Add Google account now to setup the account before proceeding to step 5. If desired to proceed to step 5 without setting up a Google account, tap Continue.
If presented, enter the current PIN, password or pattern.