How do I use cmd prompt to change all files in all subfolders?

I know that I can easily change the filetype of all files within a Windows folder by opening an elevated command prompt within that folder and typing "ren * *.jpg" or whatever other filetype I want to change it to, but how can I modify this command so that it renames all files in the current folder, but ALSO, in all subfolders?

 

Maybe this can help: https://www.windows-commandline.com/rename-file-extensions-bulk/

I didn't test it so can't say if it works.

 

http://hp.vector.co.jp/authors/VA014830/english/FlexRena/
direct download

Code:

http://download.cnet.com/Flexible-Renamer/3001-2248_4-28799.html?hasJs=n