linux - How to change the password of a (vsftpd) FTP account when 'passwd' isnt working

Kinda newbie here,

I have a server which uses vsftpd.
I changed the password of user 'aa' from the root account with 'passwd aa', which changed the SSH password for user 'aa', but not for his FTP account.

I can't seem to find much other info on changing a vsftpd password.