Have old forum and want Converting SMF 2.0 RC3 forum to 2.0.19, is that possible and how?
Just applying full upgrade 2.0.19 and beforehand deinstall mods?
https://wiki.simplemachines.org/smf/Upgrading
And yes, at least I would start with taking good thorough backups, and uninstalling any mods, before attempting the upgrade.