Hard Reset ZTE Nubia Z7 Mini

First method:

1. Turn on the device.
   
2. Next go to main screen, and press Menu button.
   
3. Now choose: Privacy -> Factory data reset.
4. Then read the disclaimer, then press Reset.
5. After that select option Erase everything.
6. Afterwards your phone will reboots.

Second method:

1. Power off the phone.
   
2. Then press and hold Volume Down + Power button.
   
3. Press Menu button to enter the Recovery Mode, when you see triangle with Android green man.
   
4. Now from the menu choose option "Wipe Data/Factory Reset" using Volume Down to browse option, and Power button to confirm.
5. Next accept option "yes" -> use Volume buttons to scroll to, and Power button to enter.
6. After that press Power button to accept option "reboot system now".

WARNING !
Hard Reset will erase all of your data
All described operations you are doing at your own risk.