Hard Reset HTC One S

First method:

1. Power off the cell phone by holding Power button.
   
2. Press and hold Volume Down and then press and hold Power button until you see three Android images.
   
3. Now select option "FACTORY RESET" to browse options use Volume Down and Volume Upbutton, and to choose option Power button. 
4. Device will reboot itself.

Second method:

1. Go from Menu to Settings next Backup & reset.
2. Find Reset phone and select it.
3. If you want delete all data (all the media) select Erase all data.
4. Press OK button.

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