It is not recommended to play this version from an existing save. This version is meant to improve upon first time players by giving them more options over the difficulty of the puzzles and combat. The max level will also be raised from 30 to 40. If you desire to download this version and continue your file, you might see yourself grinding monsters for a bit to catch up to the enemies you're facing. Overall difficulty of the game has increased by a slight margin, but not too hard. If you were playing on AUTO before this update, its recommended you start a new file if you were to download this version. From there, start a new game and choose combat difficulty easy. As of now, most of the bosses have been buffed to be much more difficult to simply let auto do the work.
Overall, I would say this update is optional. It does not add new scenes, or content to already existing files. As previous stated, it's main goal is to improve the quality of future first downloads and newcomers.