To edit class data of the window, you need to select "Background Data" and to click "Edit Parameters" button on the right window. After this, some elements of the window become active, so you could change their state, selecting new properties of window ( preview regime is locked during the edit session ):

     You can change here the next parameters/properties of application window:
1. Window background color. Click "Select New Color", to change current color. You'll be
    prompted to select new color from "System Color", or from "Custom Color", or from
    "System Brush". Select appropriate variant and set new background color for your
    window.
2. Window icon. This icon will be displayed on the caption bar of the window, if you use
    WS_SYSMENU style for your window.
3. Window small icon. This icon will be displayed on the Windows taskbar, if your
    application window will be minimized.
4. Window cursor. Use this option, if you want to see the cursor of some concrete form,
    when it moves over window.
5. Window class data. Compose necessary class styles in the right window ( "Selected
    Styles"), taking into account the description of each style you add to the list. Actually,
    for most cases, you can leave standard/default setting unchanged. Otherwise, look at
    Microsoft Platform SDK, please, for window class description and for deep understanding
    of its parameters.