As it is stated in the link, here is the layout to the related options in the boot menu.
1. Power off your unit.
2. Using a straightened paper clip, press and hold the Reset button.
3. Press the Power button to power on the unit.
4. Continue to press the Reset button until the Power button LED, USB and backup status LED, disk 1 LED, and disk 2 LED are lit
5. Press the Backup button to scroll through the boot mode options.
The unit shows the boot mode options using the LEDs, as described in the following table:
Boot Mode / Status Indicator
Normal / Power LED is lit.
Factory default / Disk 1 LED is lit. Warning: This erases ALL data on the drives!!!!!!!!
OS reinstall / Disk 2 LED is lit. This option resets your password and NIC settings
Press and release Reset button to confirm your boot menu selection.
After you confirm the selection, the NAS will shut down and reboot performing the selected task. I really hope that you did not factory default the device; because all your data will be gone, and you will have to set up the unit like it's brand new again.