Display and Change video resolutions

To display available video modes, you must use the API function EnumDisplaySettings: it gets all display setting modes available.

To change modes, you must use ChangeDisplaySettings, that changes the video resolution and color depth.

procedure TForm1.FormCreate(Sender: TObject);
var
 i       : Integer;
 DevMode : TDevMode;
begin
 i:=0;
 while EnumDisplaySettings(nil,i,DevMode) do begin
   with Devmode do
    ListBox1.Items.Add
     (Format('%dx%d %d Colors',
     [dmPelsWidth,dmPelsHeight,Int64(1) shl dmBitsperPel]));
   Inc(i);
 end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  DevMode    : TDeviceMode;
  liRetValue : Longint;
begin
 if EnumDisplaySettings
    (nil,Listbox1.ItemIndex,Devmode) then
  liRetValue := ChangeDisplaySettings
                  (DevMode, CDS_UPDATEREGISTRY);

  SendMessage(HWND_BROADCAST,
              WM_DISPLAYCHANGE,
              SPI_SETNONCLIENTMETRICS,
              0);
end;