Rename bulk files

I need to rename the '*.mp3' songs but I don't know how to change name for each and every song in a directory. Does anyone know how to do it?

I need to rename my .mp3 files like this:

Aaaa.mp3
Aaab.mp3
Aaac.mp3
Aaad.mp3
...
Aaaz.mp3
Baaa.mp3
Baab.mp3
...
...
Zzzz.mp3

I know how to change the name for a single file. But, not prefer to change each name manually.