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.
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.
150 field names? I'd pour an extra large latte, stick on my iPod, and have them changed by the end of 'Thriller'. And everything would all match up - calculations, relationships, sort orders, value lists...
This sollution would probably work if i would needed to change te data into lower cases. But my problem is that i need to change de proper cases of the fieldnames in the database for export reason. In the database i have approx 417 fiels with aprox 200 fields whitch i need to export. I have made thoose fields in proper cases so i can mark them easy when i do the export. but now thoose fields must by in lower cases too before i can export them to xml.
Export the records as a merge file. Open in excel. Use excel's LOWER function to replace the top row data. Save as xml.