updateing my db with a form containing both a textbox and a gridview

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C#

SQL

i have a form which contains one textbox and one data gridview. i have a button which saves
data into the db successfully. i have another button which i want to use in updating this record
in the db. how do i do this, please help me out

code for saving

private void btnSave_Click(object sender, EventArgs e)
{
    string StrQuery;

    try
    {
        using (SqlConnection conn = new SqlConnection(ConfigurationSettings.AppSettings["ConnectionString"]))
        {
            conn.ConnectionString = "Data Source=user-PC;Initial Catalog=MUCGPROJECT;User ID=sa;Password=mike";
            using (SqlCommand comm = new SqlCommand())
            {
                comm.Connection = conn;
                //conn.Open();
                for (int i = 0; i < dgvDistrict.Rows.Count; i++)
                {
                    StrQuery = @"INSERT INTO DistrictnT VALUES ('" + this.txtDistrict.Text + "', '" + dgvDistrict.Rows[i].Cells["clmTowns"].Value + "');";
                    comm.CommandText = StrQuery;
                    conn.Open();
                    comm.ExecuteNonQuery();
                    conn.Close();
                }
                cleardgv();
                MessageBox.Show("Record is successfully Added");
            }
        }
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message);
    }
}