Similar to the firmware upgrade process, simply login to the Home page, scroll to the bottom of the page and find the Browse button. Then find your configuration file on your local system and Upload.
If the file does not upload it may be due to a formatting error. The configuration file can only be modified using a standard text editor like MSWord or TextPad. Notepad and other text editors are known to add return charaters.
If all else fails you may send the configuration file to XRoads support to be re-formatted.