Do

0. Get the game from https://github.com/cataclysmbnteam/Cataclysm-BN/releases
1. Unpack the game
2. Copy save and config from old game directory to the new directory
3. (Optional) Copy the mods from the old game dir

Don’t

Unpack the new game over old directory

Unpacking the game over old directory can cause duplicate JSON entry errors. If you really want to do it, make sure to delete the old data directory before unpacking the new version.

Sometimes data files are deleted in the core. New version of the game will not have those files, but unpacking an archive doesn’t delete the old files. Old files will still be read and loaded, which can overwrite new entries.

Have custom mods in data/mods directory

Put them directly into mods directory, on the same level as data. This directory doesn’t exist by default, but the game will read it if it’s present.

This will allow you to copy the mods between game versions, while still allowing the “core mods” to update properly.