As of today (24 June 2011), Fedora 13 has reached its end of life for updates and support. No further updates, including security updates, will be available for Fedora 13. A previous reminder was sent on June 12th .
Fedora 14 will continue to receive updates until approximately one month after the release of Fedora 16. 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.
Fedora Project Leader