If the FAQ didn't help, try this guide:
https://steamcommunity.com/app/892970/discussions/1/3409804177175439326/

It has a lot of detailed info about the change in the save system. IIRC, using legacy worlds & characters shouldn't be a problem. Maybe a one-time effort in clicking a few buttons, but there shouldn't be anything that can break (as long as you didn't use mods).