how to export GridView to excel sheet, with structure of sheet?

i have exported my gridview to excel sheet and it's working perfect but i want to set starting row & column of data in sheet. But now i want to change the starting row,column number of data.. E.G i want the excel sheet in which data starts from row 5 and Column A. how can i do it. here is my code to print the page:

    private void ExportFile(string fileName, string contentType)
    {
        bool check = false;
        GridView1.AllowPaging = false;
        if (TruckLoadID.SelectedValue != "0")
        {
            DailyLoading1.SelectParameters["dl_date"].DefaultValue = TruckLoadID.SelectedValue;
            GridView1.Columns[0].Visible = false;
            GridView1.Columns[1].Visible = false;
            for (int i = 0; i <= GridView1.Rows.Count - 1; i++)
            {
                GridView1.Rows[i].Style["text-align"] = "center";
                GridView1.Rows[i].BorderWidth = 1;
            }
            check = true;
        }
        if (check == true)
        {
            Response.ClearContent();
            Response.Buffer = true;
            Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", fileName));
            Response.ContentType = contentType;
            System.IO.StringWriter objSW = new StringWriter();
            HtmlTextWriter objTW = new HtmlTextWriter(objSW);
            GridView1.RenderControl(objTW);
            Response.Write(objSW);
            Response.End();
        }
    }