Step 1 : Open the web browser that you use: Firefox Google Chrome or Internet Explorer and type in the IP address for your router and press Enter.
Step 2 : A window will open and then type in your routers default username and password and press Enter again Username and Password can be located on the side or bottom of your router
Step 3 : Navigate to the Wireless SecurityNetwork Security Settings Tab and open to locate or change your WEP or WPA Security Passphrase. Use WPA because it provides better security.
Step 4 : Write this Security Passphrase down and put it in a safe place to access when needed.
Step 5 : Save settings and close your browser.
If you don't know or can't find the password then on the back of the router there is a reset button that you hold in for 30 seconds and it will reset the router to factory settings and the routers address is usually on the bottom of the router.
Go into the Network and sharing center and next to the little house click on Home network then click on the top selection Home network then click on View or change HomeGroup settings them select view or print the homegroup password and there it is.