using System;

using System.Collections.Generic;

using System;

using System.Linq;

using System.Xml;                   

using System.Xml.Linq;

using System.Collections; 

using System.Collections.Generic;

using System.Data;

using System.Data.DataSetExtensions;

using System.Data.Linq;

using System.Text;

using System.Text.RegularExpressions;

using System.Xml.Serialization; 

using System.IO;

using System.Globalization;

using System.Diagnostics;

using System.Collections.Concurrent;

public class Program

{

    public static void Main()

    {

        string input = @"

<OTPC>

  <OTPCDATA>

    <PROGRAM>LOT676-Q1T2-24 RevB @MC1 PVDB Version 3.8</PROGRAM>

    <TOTAL_QTY>54123</TOTAL_QTY>

    <PASS_QTY>60866</PASS_QTY>

    <FAIL_QTY>3257</FAIL_QTY>

    <FILE_DATE>7/29/2016 10:05:47 AM</FILE_DATE>

    <FILE_TIME>10:05:47</FILE_TIME>

    <STATUS>0</STATUS>

  </OTPCDATA>

​

</OTPC>";

        XDocument doc = XDocument.Parse(input);

        doc.ToString().Dump();

        var elements  = doc.Descendants("OTPCDATA")

            .Where(x=>(string)x.Element("STATUS") =="0")

            .Select(x=>x.Element("STATUS")); 

        foreach(var element in elements)

        {

            element.Value = "1";

        }

        doc.ToString().Dump();

    }

}