How to change passwd from roundcubemail

I follow the tutorial http://www.howtoforge.com/virtual-u...x-courier-mysql-and-squirrelmail-ubuntu-10.10. I implemented roundcubemail as webmail. I want the users change the password from webmail roundcubemail.

I change the file /usr/share/roundcubemail/plugins/password/config.inc.php:

....
$rcmail_config['password_driver'] = 'sql';
$rcmail_config['password_confirm_current'] = true;
$rcmail_config['password_db_dsn'] = 'mysql://userass@localhost/mail';
$rcmail_config['password_query'] = 'UPDATE users SET password=%p WHERE email=%u AND password=%o';
....


And...

/usr/share/roundcubemail/config/main.inc.php:

// PLUGINS
// ----------------------------------

// List of active plugins (in plugins/ directory)
$rcmail_config['plugins'] = array('password');

But not found...Can I help me please??