Hard Reset ZTE Grand S3

First method:

1. At first hold down the Power key to turn off the mobile phone.
2. Then press and hold together the Volume Up + Power button for a couple of seconds.
3. You can release held keys when you see an Andoid image on the screen.
4. Afterwards press the Power key to enter Recovery Mode.
5. Choose "wipe data/factory reset" by using Volume buttons to navigate and Power key to confirm.
6. Select "Yes--delete all user data". Use Volume Down button to scroll and Power button to select.
7. To restart the phone select "reboot system now".
8. Success! The hard reset is done!

Second method:

1. Turn on the phone by using the Power button. 
2. Then from Main Menu go to Settings and then to Backup & reset.
3. Choose the Factory Data Reset.
4. In the next step tap Reset Phone. 
5. Select Erase Everything if you are sure you want to clear all your data. 
6. Well done!

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