You need to know how to use Mac OS terminal app:
- Open Terminal.app, type cd and then drag and drop the Folder containing the files to rename into the Terminal window.
- If needed, confirm you’re in the correct directory, type ls and hit enter. You will see a list of all files in the directory.
- Paste this code and hit enter:
for f in *; do mv "$f" "$f.tmp"; mv "$f.tmp" "`echo $f | tr "[:upper:]" "[:lower:]"`"; done
If needed, confirm that all your files are renamed to lowercased, type ls and hit enter again.