You can use the upgrade feature in the Fireware XTM Web UI to downgrade the device to an earlier version.
In Fireware XTM v11.7 and higher, if you use the Fireware XTM Web UI upgrade feature to downgrade the version of Fireware XTM OS, the downgrade process resets the configuration to factory default settings. The downgrade process does not change the device passphrases and does not remove the feature keys and certificates.
If you have a saved backup image, the recommended method to downgrade an XTM device to an earlier version of Fireware XTM OS is to restore the XTM device backup image. For more information, see Downgrade Fireware XTM OS.
Do not use this procedure to downgrade a device that currently runs a version of Fireware XTM OS lower than v11.7. If you want to downgrade a device that currently uses Fireware XTM OS v11.6.x or lower to an earlier version and do not have a backup image, you can use the WSM Quick Setup Wizard and recovery mode to downgrade the device. For more information, see the WatchGuard System Manager Help or User Guide.
If you do not already have it, install the older version of Fireware XTM OS on your management computer
After the downgrade, the network and security settings are reset to factory default settings, but the admin and status management account passphrases are not reset. You must connect to the device on Eth1, with the default IP address 10.0.1.1 to manage it. For more information about the factory default settings, see About Factory-Default Settings.