@alexamore90 Updating FOG is a normal process of fog administration. I agree its been quite a while since the last update but the process is the same. FOG 1.5.10 should be released soon, but until then the FOG developers are suggesting that people upgrade to a pre release but stable version of the development release.
When you installed fog if you use the git method to download the installer files then upgrading is easy and you will not lose any configuration settings. To do the upgrade its pretty easy, to perform a dev-branch upgrade there is one more step.
In your case if you are on FOG version 1.5.9 and you use the git method you would simply change to the base of the install directory (typically in /root/fogproject) and issue these commands on the fog server.
cd /root/fogproject
git pull
git checkout dev-branch
git pull
cd bin
./installfog.sh
The git checkout dev-branch command is what changes the installer to use the 1.5.9.115 (or later code base). When 1.5.10 is released you would simply replace that line with to go to the master code base with git checkout master and issue the same commands.
The installer installfog.sh will look at all of the answers you provided when fog was installed and use them during the reinstall.
After you update to the 1.5.9.115 dev release you will need to once again update the FOS Linux kernel to 5.15.x series (FOG WebUI->FOG Configuraiton->Kernel update, as well as recompile the latest version of iPXE using this tutorial https://forums.fogproject.org/topic/15826/updating-compiling-the-latest-version-of-ipxe when you complete these after steps you will be at a level that FOG 1.5.10 will be when its released. The above install process will make sure your FOG install will support the newest hardware released by the hardware manufacturers.
You say that you have 3 FOG servers you really should update them all to be on the same release or you won’t have the fix for the non-movable recovery partition that Microsoft created.