[Plugin: MD5 Password Hashes] Revert all phpass to MD5

Hi, first I want to tell that this is awesome product that enabled me to remove all errors in my database but still there are users that didn’t log in for a while and I would like to revert their pass a swell to MD5.

Can someone explain me how to do that manually?

http://wordpress.org/extend/plugins/md5-password-hashes/