To sign in/out of additional user accounts set up on the device, view this info.
Swipe down on the Status bar (located at the top).
Alternatively, access the lock screen by pressing the Power button (right edge of the device) to turn the screen off then press again to turn back on.
Tap the Manage Users icon (upper-right).
Tap the appropriate account name.
The device logs out of the current user account and into the selected account.