The warning above regards the virus definitions database. To get the latest, just run
You might need to adjust freshclam.conf beforehand if you've never run freshclam in the past. In the future, you can run freshclam from a cron job or as a daemon to keep the definitions up-to-date. Regarding your other comments, when you need to do it, it should be possible to upgrade each of amavis' components (clamav, spamassassin) separately. I don't use Fedora, but I don't believe they all come packaged together in a single RPM.