Yes, it seemed strange to me.
But in a conversation I had with them, they told me that they provide paid installation package for AcyMailing version 5, if I have an account in their website.
They also told me to use Chrome developer tools to create a custom CSS live on the website, and when I will finish it, I just copy the code and add it to Joomla template custom CSS file.
But with the help of the template providers. 🙂
I regretted deleting the old version. if I knew, I wouldn't do that!