<?xml version="1.0" encoding="UTF-8"?>
<persons xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
	<person>
		<name>Khelder</name>
		<age>21</age>
	</person>
	<person>
		<name>Redlehk</name>
		<age>25</age>
	</person>
</persons>

using System;
using System.Xml;

namespace XmlTest
{
	class XmlTest
	{
		[STAThread]
		static void Main(string[] args)
		{
			// Load the Xml document
			XmlDocument xmlDoc = new XmlDocument();
			xmlDoc.Load("person.xml");

			// Create an XmlTextWriter from the document
			XmlTextWriter writer = new XmlTextWriter("person.xml", null);
			writer.Formatting = Formatting.Indented;

			// Loop through each person
			XmlNodeList personList = xmlDoc.GetElementsByTagName("person");
			for(int i = 0; i < personList.Count; i++)
			{
				XmlElement person = (XmlElement) personList[i];

				// Get the person's name
				XmlNodeList personNameList = person.GetElementsByTagName("name");
				XmlElement personName = (XmlElement) personNameList[0];

				// Get the person's age
				XmlNodeList personAgeList = person.GetElementsByTagName("age");
				XmlElement personAge = (XmlElement) personAgeList[0];

				// Compare the data
				if (personName.InnerText == "Redlehk")
					personAge.InnerText = "44";
			}

			// Write the changes
			xmlDoc.WriteContentTo(writer);
			writer.Flush();
			writer.Close();
		}
	}
}