As of 30th July 2013, Fedora 17 has reached its end of life for updates and support. No further updates, including security updates, will be available for Fedora 17. A previous reminder was sent on July 3rd .
Fedora 18 will continue to receive updates until approximately one month after the release of Fedora 20. The maintenance schedule of Fedora releases is documented on the Fedora Project wiki . The Fedora Project wiki also contains instructions  on how to upgrade from a previous release of Fedora to a version receiving updates.