Btw, the FTP users are SSH users too and are listed in the passwd file.
Security-wise, this is not so good.
Anyway, if you have the name of your ftp/ssh user for which you have forgotten the password, just do (as root)
passwd theUser #replace theUser with the actual username, as listed in /etc/passwd
So don't change the password of the user "ftp", which seems to be a generic user for your ftp service.