Hard Reset SAMSUNG G310 Galaxy Ace Style

First method:

1. Switch on your phone.
   
2. Scroll to Settings -> User and Backup -> Factory Data Reset.
3. Accept informations in your device.
4. Done!

Second method:

1. Make sure, that your phone is off.
2. Then hold and press Volume Up + Power button + Home button.
   
3. Release all buttons when Samsung logo appear.
4. Then you will see menu of Recovery Mode, then release all buttons, and select option "wipe data/factory reset" with Power button.
   
5. Next choose "yes" using Volume Down and to confirm use Power button.
   
6. After that press Power button to enter option "reboot system now".
   

Third method:

1. Turn on your handset.
   
2. Next tap this code: *2767*3855#
3. After that your device will reset and restarts.

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