What is the puzzle? Downalod anfd install ST3 CS and American Acoustic. Authorize them of off you go.
The products are (relatively) easy to install, certainly compared with some other manufacturers.
Exactly what have you installed so far and what problem did you run into? If you still have the download files (a back-up is always recommended) you can use those for the sounds libraries. Or, I'm pretty sure, just copy them over from your old system.
When you Register a product with a sounds library, that library is available for download for 180 days and IK Multimedia recommend that it is backed-up so that it need not be downloaded again.
PS: it would be best to change your Account Name away from an email address, to minimise the chance it being harvested by web bots and you receiving all sorts of 'special offers' etc from all over the place for years and years. You can change it here:
https://www.ikmultimedia.com/userarea/account/