In order to hard reset a O2 XDA Serra, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
O2 XDA Serra device will be brought back to the default configuration of a brand new device.
1. Turn off the device.
2. Press'n'hold the Volume Down and Enter buttons.
3. Pick up the Stylus. Use it to press the Reset button hidden in the hole on the bottom of device.
4. Wait for your phone to finish resetting data. Done.