In order to hard reset a Acer Liquid Z5, 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 Z5 device will be brought back to the default configuration of a brand new device.
1. Switch off the phone, then press and hold Power button until it vibrates.
2. Now release the Power button and press'n'hold Volume Up + Volume Down for a moment.
3. In order to confirm operation "Clean Boot", press Camera button.
4. Your phone is now restored to its factory default.