To start press and hold the Windows key & R on your keyboard, this will open up a window, type cmd and press OK.
In this new window, type ipconfig and hit enter, this will display some more text. Look for Default Gateway. Enter the IP address displayed next to this, in the address bar of your chosen web browser.
Login to your router, typically (Unless changed) your credentials will be:
Password: sirusSTL.. (Your account number).
Once logged in, navigate to wireless security settings. and find the password option. Where it says the password, enter your new chosen one and click save. Then Reboot the router.
*You will have to reconnect any wirelessly connected devices*