I also installed 2019 as an upgrade to a previous 2018 installation.

The installer did not overwrite my existing 2018 installation, but renamed my existing 2018 application to "Band-in-a-Box-32bit.app" and left it sitting next to the new version.
So both versions can peacefully coexist on the same system.

As Mike said there may still be some shared preferences between the two versions, but I think most of that has been worked out.
Personally I would not delete the old version of the 2018 app, until I was sure how 2019 gets along on your machine, especially if you are in the middle of any projects.

It is still a completely new release, so you may encounter some small glitches or something that does not work as expected on your particular system.

I'm sure that any existing problems will be fixed by PG Music, but in the meantime the old application only takes up less than 80 Megs of disk space, so there really isn't any compelling reason to be in a rush to delete it.

Of course this is only my opinion, so you can take it for what it's worth.
Hopefully this helps.

- Jay

MacPro 5,1/12 core@3.46GHz -- OS X 10.14.6 -- ATI 7970 -- 32 Gig RAM -- Crucial 500GB OS SSD -- Samsung EVO 1TB Audio/Sample SSD -- BIAB 2023 -- Logic Pro X -- Cubase Elements 11 -- Too many plugins