With this webmin panel ou can modify the Pure-FTPd users database usually called /etc/pureftpd.passwd This users database allows the server to have virtual users differents from the system accounts users. Do verify that the -lpuredb:/etc/pureftpd.pdb option is set in your Xinetd configuration. You can modify your Xinetd configuration using the "Pure-FTPd configuration" panel of this module. And verify that your Pure-FTPd program has been compiled with ./configure --with-puredb otherwise the Virtual users feature is not avalaible through the Pure-FTPd server.
To disable options, just leave blank fields and/or set the value to zero (0) if already set.
Any changes you make will take effect immediately for new FTP sessions.