Syslog-ng Store Box (SSB) can not upgrade from a Feature Release (FR) to an Long-Term Support (LTS) release within the same major version.
Example: 6.1.0 cannot be upgraded to 6.0.1.
LTS versions can upgrade to FR releases, please read the latest SSB Release Notes and Admin Guide to know which versions can be upgraded to which.
FR releases can be upgraded to LTS when moving from one major version to another.
Example: 5.3.0 can upgrade to 6.0.1.
Please read the latest SSB Release Notes and Admin Guide to know which specific versions can be upgraded to which.