Download excel file on client side using webservice and jquery ajax

[WebMethod]
    [ScriptMethod(UseHttpGet = false, ResponseFormat = ResponseFormat.Json)]
    public string ExportReport(int SelectedValue, string KeyValue, string DdlCltVal, string DdlLocVal, string DdlstfVal, int BtnID, DateTime StrDate, DateTime EndDate, int currentPage)
    {
        try
        {
            CommonFunction obj = new CommonFunction();
            DataTable dt = new DataTable();
            string rhead = "";
            if (SelectedValue != 0 && KeyValue == "0" && DdlCltVal == "0" && DdlLocVal == "0" && DdlstfVal == "0")
            {
                CourierReportController objCtr = new CourierReportController();
                dt = ListToDataTable.ToDataTable(objCtr.GetDailyReport(0, 10, SelectedValue));
                rhead = "Daily";
            }
            StringBuilder sb = new StringBuilder();
            foreach (DataColumn column in dt.Columns)
            {
                sb.Append(column.ColumnName + "\t");
            }
            sb.Append("\n");
            foreach (DataRow row in dt.Rows)
            {
                for (int i = 0; i < dt.Columns.Count; i++)
                {
                    sb.Append(row[i].ToString() + "\t");
                }
                sb.Append("\n");
            }
            string strFilename = "CourierReport_" + rhead + ".xls";
            string strUploadPath = Server.MapPath("userexports").ToString();
            File.WriteAllText(strUploadPath + "\\" + strFilename, sb.ToString());
            return strFilename;         
        }
        catch (Exception ex)
        {
            throw ex;
        }
    }

$('#btnExport').click(function (e) {
 var data= JSON2.stringify({
                    SelectedValue: selectedValue,
                    KeyValue: KeyValue,
                    DdlCltVal: ddlCltVal,
                    DdlLocVal: ddlCltVal,                    
                    DdlstfVal: ddlstfVal,
                    BtnID:btnid,                    
                    StrDate: strDate,
                    EndDate: endDate,
                    currentPage: currentPage
                });
            $.ajax({
                    contentType:  "application/json; charset=utf-8",
                    type: 'POST',                       url:'http://localhost:8043/Modules/CourierReport/services/CourierReport.asmx/ExportReport',
                    dataType: 'json',
                    data:data,
                    success: function(result){
                    alert (result.d);
                    //should i do any thing here?
                    },
                    error: function(error){
                    alert("error");
                    }
                });
                    return false;
});