private void button4_Click(object sender, EventArgs e)
        {
            Startupmanager startupmanager = new Startupmanager();

            panel2.Controls.Clear();
            panel2.Controls.Add(startupmanager);
        }
 private void button4_Click(object sender, EventArgs e)
 {
     Startupmanager startupmanager = new Startupmanager();
     panel2.Controls.Clear();
     panel2.Controls.Add(startupmanager);
 }