Go to your router' admin page, and enter user name / password. From there, you will be able to change WiFi security settings.
Google/Bing with your router make about how to access this page. As for the password, you should have records on it somewhere. If not - reset your router (this will reset, in most cases, WiFi secirity as well), and start from scratch.
You won't get help here about "I forgot my router password, can you help?"