In order to hard reset a GFive U855, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
GFive U855 device will be brought back to the default configuration of a brand new device.
1. Turn on the phone.
2. Select Settings and Restore Settings.
3. Tap in the security password, 1122 by default.
4. Wait for the phone to restart. Voila.