Downgrading is currently not supported!
It is not safe to install a previous version, because the database will most likely not be compatible. Therefore, it is recommended to take a backup of the database before upgrading.
Should something not work out as expected, you need to restore the backup and then go back to the previous version.
If you need to downgrade after running for a while, create an issue or meet on matrix/gitter. We should be able to find a way.