I purchase (I believe) the lifetime updates package back in 2017, and I was wondering if I was entitled.
When I go to my account, I can only see v1.4.8 to download.
Yes, you are right,
In our server still is the version 1.4.8 for the download.
Just download, install and register your theme and you will see a notice that new version is available, then simply update it, from the WordPress Dashboard->Update menu.