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Save it on the old version in an open space where you can access map, inventory etc. Then load it on new version.
This is no longer really necessary as of 0.19.2. You can load pretty much any save file during any event etc. Only exception is the battle minigame.

This is to apply new changes and variables. If you load a savefile where you're playing the battle minigame, you'll simply get a load of errors.