Acyba is completely recoding Acymailing and that became version 6. After a major change in v6 they changed the version number into 7, but in fact it is an ongoing development of v6.
V5 and v7 each use their own set of database tables. So you can install both on your site. That way you can continue to use v5 and start to get familiar with v7. Make sure you attach your license to v5 and whenever you start using v7 in production you can unlink your license from v5 and link it to v7 instead.
You'll find all the v7 documentation here: https://docs.acymailing.com/.
The future of Acymailing is at v7, so yes I highly recommend to migrate to v7.