Well, there is not a simple way to do this in Filemaker with adding additional calculating fields using either the Lower or Proper functions.
But here's the way I might handle this.
Make a cloned database (exact copy without records). Then in the orginal database create a field (or the number of fields you might need) using the Proper or Lower function (that returns corrected data from your upper case fields). Then, import into your cloned database the records from your old db, substituting the fields that contained the upper case data with the field(s) containing the lower case data.
Hi, Jeff! I'd just export/import as you say. Find All, Sort, Export, use editor to change them all to WhateverCase you want and save, Import back and replace, and you're done. Just don't let anyone access the db while you do this and back it up first to verify data and in case something goes awry. Good luck! --ST