Just open your old 11.3 (or even 11.1 or 11.2) appliance, go to the Start tab and click on the “Upgrade” button in the bar at the top.
After that, we'll perform the magic — upgrading your appliance to 11.4!
What exactly “magic” means here? We try to change repositories to their 11.4 equivalents and sometimes add or remove few packages to ensure everything works smoothly. You can see what exactly was done in the log accessible from the bar at the bottom of the Start tab.
Sometimes the upgraded appliance will need some more tweaks to make it work. Just inspect the log, see what was changed, and apply any additional adjustments. Let us know what you had to do on our forum or mailing list so we can improve the upgrade in the future.
If you are not satisifed with the upgrade, you can always revert to original version by clicking the “Undo upgrade” link.