Well...first can you get into the routers setup page?
If not and you forgot the password...there should be a reset button on the unit...
What is the model number of the router?
Some router reqire you to hold the reset while powering up the router to get it back to factory settings.
Then you would enter the default user name and password to get on the setup screen..
1)Open the web browser that you use: Firefox,Google Chrome,IE,or Opera and type in the IP address for your router,and press the Enter key. http://www.routeripaddress.com/< Router ip addresses can be found here
2)A window will open and then type in your routers default username and password,and press the Enter key again http://www.routerpasswords.com/< Router usernames and passwords found here
3)Navigate to the Wireless Security\Network Security Settings Tab and open it to locate or change your WEP or WPA Security Passphrase. Use WPA because it provides better security.
4)Write this Security Passphrase down and put it in a safe place to access when needed.