How to Download All 45 Themes Outside of the 5 Given?

The plugin is working good on my site.

I am wondering, however, where the rest of the themes are. I see over 45+ themes at https://pressbooks.com/themes/ — but the plugin only came with 5 (which are working fine on my site).

But I don’t see any option to download more themes within the plugin, anywhere on www.ads-software.com nor on your site (https://pressbooks.com/themes/).

So how do I download more themes outside of the five that came with the plugin?

https://www.ads-software.com/plugins/pressbooks/