An upgrade of Composer means that you are upgrading from an earlier version of Composer to a newer version of Composer . This includes uninstalling the previous version and installing a later version. To learn more about upgrades, see Upgrade Composer.
A clean installation of Composer means that you are installing a new version of Composer from scratch. The Composer metadata is empty and contains no information. This either means that the PostgreSQL is a fresh install as well or that the zoomdata database is empty.
A supported upgrade of Composer allows users to continue working in an existing Composer environment while a clean installation of Composer is completely new. For clean installation instructions, see Install Composer.
The main difference between an upgrade and clean installation of Composer is whether or not the PostgreSQL is from an existing Composer installation or is new and empty.