In order to hard reset a Acer Liquid S1, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Acer Liquid S1 device will be brought back to the default configuration of a brand new device.
1. Please, power off the phone first.
2. Second, press and hold together Volume Down + Power button until the phone vibrates.
3. Quickly release Volume down and press Volume up and you will see a new menu on screen.
4. Next, use Volume buttons to select "Recovery" option.
5. Choose the "Wipe data/factory reset" from the Recovery mode menu. Use Volume buttons to scroll to options and Menu button to confirm.
6. Last, accept operation by choosing "yes - delete all data".
7. Select the "reboot system now" option.