First before you flash it's smart to have a backup of the systems configuration, you can't be safe enough.
Note: Do not store the XigmaNAS config file on your server storage, keep it somewhere else safe!
Navigate to the System: Firmware page and click the Enable firmware upload button.
Click the Browse button (Bladeren on dutch system) and navigate to where you stored the previously downloaded .IMG.XZ file.
Once the file is in the firmware image file window, click the Upgrade firmware button.
A message will indicate the upgrade installation is being performed and XigmaNAS will reboot once this is completed: “The Firmware is now being installed. XigmaNAS will reboot automatically.”
Once the reboot is completed, you can login back into the XigmaNAS WebGUI.
Note: If, for some reason you cannot connect to XigmaNAS, connect a screen to your XigmaNAS server (if not already connected) and verify the network settings using the console menu. It’s possible that with an new release, the name of your LAN card changes (FreeBSD new NIC drivers for example), of course this happens seldom if at all.
The upgrade procedure may upgrade the configuration file. It should work without problem, but it is a good idea to verify your settings. Browse to several screens in your XigmaNAS and verify that items such as the network and disk configuration are still configured as you previously did configure.