Code:
private void Load_ThuTu()
{
string HienTai = DuLieu._DataTable("SELECT cThuTu FROM TableXYZ WHERE ID=" + Request.QueryString["ID"]).Rows[0][0].ToString();
string TuongLai = null;
if (Request.QueryString["do"] == "up")
TuongLai = DuLieu._DataTable("SELECT TOP 1 cThuTu FROM TableXYZ WHERE cThuTu<" + HienTai + " ORDER BY cThuTu DESC").Rows[0][0].ToString();
else
TuongLai = DuLieu._DataTable("SELECT TOP 1 cThuTu FROM TableXYZ WHERE cThuTu>" + HienTai + " ORDER BY cThuTu ASC").Rows[0][0].ToString();
DuLieu._RunNoReturn("UPDATE TableXYZ SET cThuTu=" + HienTai + " WHERE cThuTu=" + TuongLai);
DuLieu._RunNoReturn("UPDATE TableXYZ SET cThuTu=" + TuongLai + " WHERE ID=" + Request.QueryString["ID"]);
Response.Redirect(Request.Path);
}
Có thể làm theo 2 cách. QueryString or RowCommand để lấy Mã 
Load dữ liệu lên thì chỉ cần order by cột thứ tự