How to keep your Operating System up to date could be different, depending on the OS, which you did not specify.
Usually, you could configure automatic updates, so you don’t have to search for the updates manually. Updates include service packs, hot fixes, etc…
If it is a windows machine, you could also go to the <a href=”http://update.microsoft.com/microsoftupdate/v6/default.aspx?ln=en-us”>Windows Update</a> site.
About vulnerabilities found in other programs, <a href=”http://forum.kaspersky.com/index.php?showtopic=68831″>this article on the Kaspersky forums</a> offers some guidance.