Hard Reset HTC Windows Phone 8S

First method:

1. On the Start screen, slide to the left.
2. Tap Settings > About (informations)
3. Tap Reset your phone, and then tap Yes.

Second method:

1. From the Main Menu choose Settings.
2. Then tap About and select Reset your phone.
3. Confirm the whole operation tappind Yes.
4. Turn off your phone.
   
5. Press and hold the Volume Down button, and then briefly press the Power button. Release the Volume Down button when you see an icon on the screen.
   
6. Then press the following hardware buttons in this sequence: Volume Up > Volume Down >Power > Volume Down
   

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