Upgrade SFOS 16.05.3 MR-3 to SFOS 18.5.3 MR3-Build408 or SFOS 19.0.0 GA-Build317


We have a Sophos XG115 in place running on SFOS 16.05.3 MR-3.

The Firewall itself is showing us Update HW-17.5.16_MR-16.SF300-830 as latest update release.
Unfortunately, we do not have a support subscription fpr In-Product Fimware download.

In MySophos there are only the updates SFOS 18.5.3 MR3-Build408 or SFOS 19.0.0 GA-Build317 available.
For my understanding, the upgrade path does not allow an update to this versions coming from our old firmware.

Could you please give us any advice how to upgrade the firmware due to CVE-2022-1040?
Is it possible to jump directly to one of the downloadable versions or do we have to perform some firmware steps before?
If needed, where can we download an older firmware version?
Are there any major changes or reconfigurations needed between the firmware versions?

Kind regards and thank you in advance

Added TAGs
[edited by: emmosophos at 5:49 PM (GMT -7) on 13 Jun 2022]