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

[BlackScarletLove]

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?

 

[American Zombie]

I would just use this - Bulk Renamer Utility

According to the site, Bulk Rename Utility is free of charge for personal, private use, at home.