With this feature you can change the password(s) for your (different) user name(s), depending on your account features.

Click on the specific username, and type the password you wish to change to.
You must then retype the password for confirmation.

The Mysql user requires the password you need to log into your mysql databases, if activated.

The plusmail user is the login/password combination for this web control panel (yourname.com/cgi-bin/plusmail).