You can't reset JUST the password if you've forgotten or don't know. You'd have to do a hard reset which is holding the reset button down for 10 seconds (I think it was that long).
But this will erase everything and restore your device to factory defaults. After you do that, both of the default logins should work. I'd recommend securing your router's Wireless and other settings afterward.
I don't know about the DNS, but there's probably a setting in there somewhere. Don't know because I set mine up to be a bridge/modem.