From the comments elsewhere in this forum you may not want the latest version as it has some problems in demanding it's own toolbar in Firefox and only being movable to the left of toolbars in IE. They are working on that.
If your stuck with an old version you could force an upgrade by uninstalling completely via Control Panel/Add or Remove Programs (XP) Programs/Uninstall a Program (Vista).
If it isn't listed separately click "McAfee Security Center" then select it for removal.
Then either go to your online account or http://www.siteadvisor.com/