Answer by Martin Prikryl for How to change FTP password from command line?

Some FTP servers implement proprietary commands to change password. In Windows command-line FTP client, you can execute them using the QUOTE command. The same on *nix.

Titan FTP server:

QUOTE SITE PSWD "<old_password>" "<new_password>"

WS_FTP server:

QUOTE CPWD <new_password>

Older versions of WS_FTP server used:

QUOTE SITE CPWD <new_password>

Reference: Changing account password with WinSCP.