cmd - How To Rename The Extension of All The Files In A Directory Tree With Command Prompt -

i'm trying rename extensions of files in directory , tried using
ren *.[old]* *.[new] renamed files in current directory. know how rename extensions of folder , of sub-folders well?

for /r /d %i in (*.*) ren %i\*.old *.new

the /d select directories only, , /r recurse subdirectories.