Perform a soft, factory, and alternate master reset of the device.
INSTRUCTIONS & INFO
From the home screen, swipe down on the Notifications bar with two fingers.
Tap the Settings icon.
Scroll to, then tap Backup & reset.
Tap Factory data reset.
Tap RESET PHONE.
Tap "ERASE EVERYTHING."
If unable to reset the device using the above steps, try the alternate master reset method by first powering the device off. Note: Do this by pressing Power/Lock key > Power Off
With the device powered off, press and hold the Power + Volume up keys until the white ZTE screen appears.
Press the Volume down key to show the Android system recovery menu.
Press the Volume down key until "wipe data/factory reset" is highlighted, and then press the Power key.
Press the Volume down key until Yes -- delete all user data is highlighted, and then press the Power key.
After the data wipe is complete, with "reboot system now" highlighted, press the Power key to reset the device