Unfortunately Switchvox does not offer a method in which a customer can downgrade or roll back to a software version previously installed, the only method we have is reinstalling desired older version using a ISO.
Please note that backups can only be restored on the version that they were created, as such, if you need to downgrade or roll back to a desired version, you will need to use a backup that was created on that software version that you wish to install or rebuild the configuration from scratch.