Hard Reset SAMSUNG I257 Galaxy S4 mini

First method:

1. Turn on your cell phone.
   
2. Now goto Settings -> User and Backup -> Factory Data Reset.
3. Confirm all information on your screen.
4. Done!

Second method:

1. First you should power off your device.
   
2. Next press and hold Volume Up + Home button + Power button until you see logo of your phone.
   
3. Then from the menu choose option "wipe data / factory reset" using Volume buttons to scroll options, and Power button to confirm operation.
4. Now select "Yes -- delete all user data", and confirm that.
5. After that press Power button to accept option "reboot system now".
6. Success!

Third method:

1. Switch on device.
   
2. Dial or press number to call: *2767*3855#
3. That number code will force format on device.

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