function DynamicResolution(X, Y: Word): BOOL;
var
   lpDevMode: TDeviceMode;
begin
   Result := EnumDisplaySettings(nil, 0, lpDevMode);
if Result then
begin
lpDevMode.dmFields := DM_PELSWIDTH Or DM_PELSHEIGHT;
lpDevMode.dmPelsWidth := X;
lpDevMode.dmPelsHeight := Y;
Result := ChangeDisplaySettings(lpDevMode, 0) = DISP_CHANGE_SUCCESSFUL;
end
end;

PRocedure TForm1.Button1Click(Sender: TObject);
begin
if DynamicResolution(640, 480) then
ShowMessage('Now is 640*480');
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
   if DynamicResolution(800, 600) then
      ShowMessage('Now is 800*600');
end;