var wnd = win32.FindWindowA(null, "窗口标题");
 Int32 wndStyle = win32.GetWindowLong(wnd, win32.GWL_STYLE);
 wndStyle &= ~win32.WS_BORDER;
 wndStyle &= ~win32.WS_THICKFRAME;
 win32.SetWindowLong(wnd, win32.GWL_STYLE, wndStyle);

const int WS_THICKFRAME = 262144; 
const int WS_BORDER = 8388608;

[DllImport("user32.dll")]
public static extern IntPtr FindWindowA(string lpClassName, string lpWindowName);
[DllImport("user32.dll")]
public static extern int GetWindowLong(IntPtr hWnd, int nIndex);
[DllImport("user32.dll")]
public static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);