If you click on the Settings-Button you enroll a more-featured settings-window. Primarily you may want to change the update-frequency of KDiskFree. Just use the scrollBar to select the appropriate frequency. If you want to DISABLE the auto-update-feature, you only have to select 0 as your update-frequency. To force an update, just press the Apply-Button.
There you can enable/disable the shown columns of your device-Overview. If you don't want to see the Filesystem-Type (which maybe is not of that interest to you, because it doesn't change every five seconds) you may just click on the Type-Header in your settings-window, so the checked-icon under Type changes to a crossed-out-icon. To enable it, just press the Type-Header again and the crossed-out-icon becomes a checked-icon. For convenience, you may also double-, mid- or right-click on the icons to get the same effect.
There is also a LineEdit to enter the preferred FileManager used when you click on the mountpoint of a device. The %m will be substituted with the actual mountpoint.
To reset all to the default values, just click on the Defaults-Button