You could also reset the router and setup a new password!
How to reset wireless router password?
The location of the reset button varies depending on your router make and model, but it is usually located in a small pin hole on the side or back of the unit. Insert a small pointed object into the hole until you feel press down.(Hold the button down for 10 to 20 seconds.) Your router is now set back to its factory default settings.
Sign in and configure the router following the reset. Connect a PC to an Ethernet port on the router. Open a Web browser and navigate to http://192.168.1.1 / or http://192.168.0.1 / or http://192.168.2.1 /. A window will pop open, asking you to sign in. On older routers, leave the username field blank and type admin for the password. On newer routers, the default username and password are both usually admin.
Navigate to the Wireless Settings tab after you've signed in and set a new administrator password. For better security, choose a password comprised of random letters and numbers. This makes it a password that is harder to guess.Write down this password and save it in a safe place for future reference.
Then in the Wireless Security Settings tab also enable WEP or WPA security so that leechers cannot jump on your wireless network.
* Use WPA if it is an option because it is more secure.