1. ACF4 and ACF5 store field data in different DB locations
2. Upgrading from v4 to v5 will launch a migration tool which will copy the data to the new location.
3. All v5 editing will not effect the old v4 data
4. Any fields created in either v4 or v5 can be exported to PHP and will work in both versions!
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users