Linux upgrade from classic 2.7 to 3.x and from Ubuntu to Centos

Since I’m moving from Ubuntu to Centos as well as upgrading the Omeka software, would it be easier to copy the folders over to the new Omeka classic 3.x version on the new Centos server from the current 2.7 version on Ubuntu?

I don’t think there’s a significant advantage of upgrading during or after the move. But, if I was doing it, I’d migrate the current version of the installation, check that everything works as expected, and then perform the upgrade. Follow these instructions.