You can control Users' maximum transfer speeds at three levels;
The Site Level provides a limit over all other levels (see Overview).
Start the Administrator Interface and connect to the Server.
At the bottom of the left pane, click the Server tab.
In the left pane, select the Site you want to modify.
In the right pane, click the Advanced tab.
Select the Max transfer speed (KB/s) check box and enter the maximum transfer speed for the site. The server will not set a maximum transfer speed if the box is cleared.
Click Apply.
Start the Administrator Interface and connect to the Server.
At the bottom of the left pane, click the Server tab.
Select the User or User Setting Level you want to configure. You may have to expand a User Setting Level to see the user you want.
In the right pane, click the Quota tab.
Select the Max transfer speed check box and enter the maximum transfer speed (in Kilobytes per second) for the user.
Click Apply.
Setting maximum concurrent connections to a Site
Setting maximum connections per User
Setting maximum connections per IP