i just plugged into the thing, and configured it for the first time... wanted to save my settings so i used the option to save all the settings to a configuration file on my computer.  did that... and opened up the file to see what settings the thing actually had configurable, and i found the following in it:

super_username=Gearguy
super_passwd=Geardog

so i googled it, and long behold here i am on this page.

My suggestion... save the config file, find the super_username and super_passwd, change those values to whatever ya want, and reload the cfg file into the router.  viola, taken care of.