That depends on what you have installed exactly and where you are with your versions.
Non distro installs are significantly harder to upgrade and get support on than the official FreePBX distro.
In my experience, upgrading has become safer than it used to be. It looks like Sangoma developers have been putting quite a bit of effort into that, especially in SNG7.
Considering that this will probably further improve with future versions, I would definitely recommend to stay relatively current and upgrade to avoid the point where nobody wants to support your old version.
But surely prepare for the worst case and keep backups ready in case your upgrade goes south and you have to do a complete reinstall, or have some money that you can spend with Sangoma commercial support if you need urgent help.
Once you are on SNG7, there is also no need for running yum updates anymore, you do everything from sysadmin on the GUI.
Running yum update on 10.13.66 Distros is also not necessary: