In order to hard reset a Acer Iconia Smart you should follow the steps listed below.
Important thing is, that hard reset will delete all data on your device, like pictures, contacts, messages, apps and more.
Acer Iconia Smart device will be brought back to the same configuration as if you bought a brand new device

Turn off your phone by pressing and holding Power button.
Then release Power button and press and hold Volume Up + Volume Down for few seconds.
Press Camera button to confirm operation "Clean Boot".
Now your phone will be restored to the factory default.