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 ***** Username and Password may also be located on the side or bottom of your router *****
3)Navigate to the Wireless Security\Network Security Settings Tab and open 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.
If you have a mac that you have already put the password into. Look in the Keychain Access application under network connections. You can reveal the password that you put in. This way you dont have to try to login to the router and/or try to finds its password also.