In order to hard reset a ZTE Grand S II, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
ZTE Grand S II device will be brought back to the default configuration of a brand new device.
1. Turn off the phone.
2. Press'n'hold the Volume Down, Volume Up and Power buttons.
3. Now select the Wipe Data/Factory Reset option.
4. Continue by selecting yes and reboot system now.