I would begin by writing a small program to first find the file(s) I was interested in, probably by doing Super Search and consulting some of the recent, promising-sounding hits, such as:

• How to find the most recent file?
• Search for oldest file in directories and its subdirectories
• How to read list of files based on date ?

Then I'd move on to renaming. If I had problems with any of the code I'd written, I'd come back, post it here, and ask for specific tips on how to make it work.