@L&LD has created a write up on multiple instruction sets useful for setting up and troubleshooting routers. Look here, then the M&M configuration. This instruction says perform Factory Reset from the GUI, located in the Administration, the Restore/Save/Upload tab. First option on the tab, check the box to reinitialize all settings.
www.snbforums.com
There is another quick way to factory reset by holding the WPS button in while turning the power on, and depending on your model, either hold it in until it reboots or until the power light cycles and goes out, then release the button.
Its advisable to perform a factory reset again after these betas have gone to release and you update to the final 386 release.