Since no one seems to know the answer to my "how do I" question, and since I'm probably not the only customer who isn't running threads 6.5, I'll answer my own question for your potential benefit (sorry for the long unedited sentence).
Infopop no longer makes available in the member area versions other than the most current. If you would like a licensed copy of a version earlier than 6.5.1.1, you must (1) fill out a support request form and (2) when asked, send in your license info and then (3) the requested software will be sent to you by email.
That's it. A bit of a hassle, but not too difficult and the support folks respond relatively quickly.
packlite