With firmware version 6.6.5 there are now two different ways to reset any WiFiRanger router to factory default settings.
If you can access your WiFiRanger's Control Panel, there is now a Reset to Factory Default button at the bottom of the Setup page. When you push the button and confirm your action the router will reset itself and then direct you to reboot it.
If you cannot access the WiFiRanger's control panel you can force a reset to factory default by a specific sequence of reboots. The sequence has been changed from previous firmware versions to minimize accidental resets. Here's the sequence to follow:
Wait 1 minute ( waiting 1:30 is smart to be safe )
Wait 2 minutes ( waiting 2:30 once again is best to be safe )
Wait 2 minutes ( waiting 2:30 for the last time to be safe )
After this last reboot it should now have the factory settings.