how to close windows forms ?

//Hide the current Form.
this.Hide();
//Created an object of GetNotificaiton From.
MainForm showNotification = new MainForm();
//show the GetnNotificaiton From.
showNotification.Show();

private void button1_Click(object sender, EventArgs e)
       {
           Form2 obj = new Form2();
           obj.Show();
           this.Hide();
       }

static class Program
   {
       /// <summary>
       /// The main entry point for the application.
       /// </summary>
       [STAThread]
       static void Main()
       {
           Application.EnableVisualStyles();
           Application.SetCompatibleTextRenderingDefault(false);
           if (new Login().ShowDialog() != DialogResult.OK)
           {
               Application.Run(new Form2());
           }
       }
   }

private void Button1_Click(object sender,EventArgs e)
{
    this.Close();
    LoginForm lf=new LoginForm();
    lf.Show();
}