If I went to a PC that had version 6.x you're supposed to be able to right-click the tray icon and "Check for Updates" but it always said I had the latest version.
Finally found this web page:
At the very bottom in fine print they tell you to manually upgrade click this link:
I went there, had to login first, but was then offered the download. Had to install it twice to get it to take, and even after it took, it then told me I had an update to apply. By the way, this is on a Windows XP SP3 machine.
This update process is obviously very buggy.