I remember I did a similar job in the past, the migration of an old release of esmith to the lastest release. Too many changes were done between the both versions. So, it was actually impossible to migrate from one to the other, that's also include step by step migration.
The only way, was to inspect after saving on non-versatile media the old configuration, just in case.
Depending of what you 've set, the major configurations are done in the /etc, some in /usr/local/etc and some others in /var
Keep in mind, as more you give informations (release, recent changes, ...) as more we can help you.