Most have a way to see and change settings in a web-browser on one of PC's connected wired (not: wireless). Read the manual to find the IP-address (like 192.168.1.101 or so).
The manual also will mention the default password for changes, but if you changed it yourself than it's your responsibility, of course. Then find out about the 'reset to factory defaults' options.
Yeah...how do I find out what my router's name/password is?