shell32.dll c# example
private static void advanceBackgroundSlider()
{
//Display the Desktop via the COM component Shell32.dll
Shell32.Shell objShell = new Shell32.Shell();
objShell.ToggleDesktop();
// Simulate Ctrl + Space to deselect anything that may be selected
SendKeys.SendWait("^( )");
// Simulate pressing Shift + F10 to open Desktop context menu
SendKeys.SendWait("+{F10}");
// Simulate pressing N to execute the “Next desktop background” command
SendKeys.SendWait("{N}");
}