MUST BE ON AN ACTIVE SILVER MEMBERSHIP ACCOUNT!

1) go to the xbox dashboard, currently signed into the silver account.
2) sign out of the account and return to the dashboard.
3) there should be a window under the home tab that says "explore xbox live" click that window.
4) once you pull up that window sign back into your silver account and click the window "what's in gold"
5) once you are there click 'A' and confirm payment (must have an active paypal or credit card on file)
after that you will have one month of gold on xbox live for free, it will not charge your account until the monthly renewal.

IF YOU DO NOT SEE THE 'EXPLORE XBOX' WINDOW ON THE DASHBOARD

1) go to settings, then language and locale.
2) change your locale to United States and then restart your xbox and repeat the steps above.

hoped this helped out.