"SITE PSWD old new"
is a non-standard extension of the FTP protocol and it is not implemented by all FTP servers. In fact, I guess that most FTP servers don't support it (and some only support it for a subset of authentication methods).
Some FTP servers might use a different command than SITE PSWD
. For example, WS_FTP uses "SITE CPWD new"
command to change the password.
Since this functionality is server-specific, our advice is to consult the documentation of your FTP server for more information.