Hard Reset SAMSUNG G3812B Galaxy S3 Slim

First method:

1. First power off your phone.
   
2. Then press and hold together 3 keys: Volume Up + Home button + Power button.
   
3. When you see logo Samsung, then release all holded keys.
4. Next select option "wipe data/factory reset" -> use Volume buttons to browse, and Power button to confirm option.
   
5. Now choose "yes" with Volume Down, and confirm with Power button.
   
6. After that press Power button, to confirm option: "reboot".
   

Second method:

1. Turn on you cell phone.
   
2. After that browse to Settings -> User and Backup -> Factory Data Reset.
3. Next please confirm info on your screen.
4. That's all.

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.