How to retrieve text from database, edit it and resend it to Database

protected void Page_Load(object sender, EventArgs e)
    {
        if (Session["Admin"] == null)
        {
            Response.Redirect("~/Admin/Login.aspx");


    }


            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);
            con.Open();


            SqlCommand com = new SqlCommand("SELECT * from AboutUsData", con);
            SqlDataAdapter da = new SqlDataAdapter(com);
            DataSet ds = new DataSet();
            da.Fill(ds, "AboutUsData");



            txtAbout.Text = ds.Tables["AboutUsData"].Rows[0]["About"].ToString();
            con.Close();

         
          




        
    }
    protected void btnSubmit_Click(object sender, EventArgs e)
    {
        
        if (txtAbout.Text.Length != 0)
        {

            string AboutText = txtAbout.Text.Trim();
         
            SqlConnection con = new SqlConnection(ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString);


            
           
            con.Open();
            SqlCommand cmd1 = new SqlCommand("INSERT into AboutHistory Values ('" + AboutText + "')", con);
            cmd1.ExecuteNonQuery();
            con.Close();



            con.Open();
            SqlCommand cmd = new SqlCommand("DELETE from  AboutUsData", con);

            SqlDataReader rd = cmd.ExecuteReader();

            con.Close();





           
            SqlCommand cmd2 = new SqlCommand("INSERT into AboutUsData Values ('" + txtAbout.Text  + "')", con);
          
             con.Open();
            cmd2.ExecuteNonQuery();
            con.Close();




            Response.Redirect("~/Pages/AboutUs.aspx");


        }