Hard Reset XIAOMI Mi 4

First method:

1. At the very beginnig hold down the Power key to switch off the device.
2. Afterwards press and hold the Volume Up + Power button for a couple of seconds.
3. When the Mi Logo appears on your screen release only the Power key.
4. Keep holding the Volume Up key until the Recovery Mode appears.
5. In this step select English using Volume keys to browse and Power rocker to select.
6. Then select "Wipe Reset" by using Volume Down to scroll and Power button to confirm.
7. Select "Wipe All Data". Use Volume buttons to navigate and Power key to select.
8. Confirm the whole process by selecting "Yes".
9. Success! The hard reset operation has just been performed.

Second method:

1. Switch on your device.
2. Afterwards go to Settings and then to Backup & reset.
3. Tap Factory Data Reset and selec Reset Device. 
4. Choose Erase Everything if you are sure you want to clear all your data. 
5. Select OK to confirm the whole operation.
6. Well done!

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