From a Home screen, tap Apps > Settings > Security.
If unavailable, tap the dropdown menu (located in the upper left) then tap Alphabetical. If still unavailable, refer to Manage App Icons.
Tap Screen lock.
If presented with "This device does not have a Google account associated with it. If you forget your PIN, it cannot be sent to you and a factory reset has to be performed to recover the device.", tap Add Google account now to setup. If desired to proceed without setting up a Google account, tap Continue.
If presented, enter the current PIN/password/pattern.
Tap Face Unlock.
Tap Set it up.
Using the front-facing camera, position face within the provided area.
Hold still for several seconds to allow image capture.
Tap Continue then tap one of the following to set up an alternate unlock option:
Enter a numeric PIN (4 to 16 digits) then tap CONTINUE.
Re-enter the numeric PIN then tap OK.
If presented, tap OK.
Draw an unlock pattern (connecting at least 4 dots) then tap CONTINUE.
Re-draw the pattern then tap CONFIRM.
If desired, tap Make pattern visible to enable/disable.
Enabled when a check mark is present.