Upgrade from 2-16-5 to 3 " There's no upgrade package available for download."

Can you try this step using curl?

You cannot just move folders around - there are many complex steps that you need to go through including file and database changes. You must use the upgrade script.

If this throws an error we may have a culprit - if not we will see if we can step through what is causing the upgrade script to halt. It is designed to halt if there are problems that will affect the installation, we just need to track down what the problem is!