My good self, master of all things IT, have managed to change 4860 jpg files into Unix Executable Files in the process of renaming them. I obviously didn't pay enough attention to the boxes needing checking

The solution is to rename the file extension, and it works. However to do this 4859 more times would take a week. Any suggestions how to do this easily and effortlessly ? The renaming program I use doesn't seem to have a reverse/reverting action and the developers haven't answered my pleas for help as of yet (5days). Heeeelp!
SHJ