Use the Replace Field Contents option in the Records Menu and you can do a batch update of your data. This cannot be undone and could modify a very large number of records all in one go, so it's not a bad idea to make a back up copy of your file first.
You can use the calculation with Replace Field Contents to remove the .jpg from this text:
Left ( Yourtable::YourField ; Length ( YourTable::YourField ) - 4 )
Aw cool...thanks so much. You have saved me from having to edit 2800 indiviual files...