Acer S500 hard reset
1.Power off the phone
2.Power on with Power + Vol down (Acer logo will appear and the phone will vibrate after 2sec.)
3.Once it vibrates, release Vol down and push Vol up
4.The phone will vibrate again, release Vol up, it will boot in recovery mode.
5.Use Vol down and Vol up to select "Wipe data/factory reset" and then use Power to select it.
6.Confirm "yes"
7.Once done, reboot the "cleaned" phone.
Here you have vide tutorial:
GSM-ABC