How to change all files extension automatically

Usually, you right click on a file and then rename it to change its extension. But what if you got so many files to be change?

Using this little trick, you can change the extension for all files in a folder automatically using the command prompt tool. As example, if you have 100 mp3 files in a folder and want to change it to .jpg file format for security, this is the command that you should use.

ren *.mp3 *.jpg

Screenshot: