To perform a complete factory reset on the device:
1. Plug in the AC charger, and make sure it remains plugged in throughout the process
2. Turn the DR2 off by pressing the power button
3. Press and hold Volume Down (-) button and the Power button. Continue holding the buttons when the lock screen is displayed, and release them when Recovery is displayed.
4. On the boot loader menu, use the Volume Down (-) button to move the selector to Wipe all user data / Factory reset, then press Power
5. After that process finishes, select Reboot system now.