A standard upgrade ensures that all packages within a major release are up-to-date, while a release upgrade upgrades from one major version to another.
However, due to technical limitations, a standard ("everyday") upgrade cannot perform the same functions as a release upgrade. The release upgrade procedure upgrades a significantly larger number of packages, often removes certain packages, and requires the user to follow additional steps as outlined in the release upgrade documentation.
What is better? Upgrade or Image Re-Installation? See Update vs Image Re-Installation.
For the latest instructions on a release upgrade from Whonix ™ 15 to Whonix ™ 16, see here.
It is very much discouraged to run the
release-upgrade command without following the release upgrade instructions for the version intended to be upgraded.