using System;

using System.Xml;

public class Program

{

    public static void Main()

    {

        var raw = @"<root>

<Attr num=""108"" name=""Title"" desc=""The title of this file."" type=""s"" ord=""1""/>

<Attr num=""108"" name=""Title"" desc=""The title of this file."" type=""s"" ord=""2"" value=""foo""/>

</root>";

        var xmlDoc = new XmlDocument();

        xmlDoc.LoadXml(raw);

        var nodes = xmlDoc.SelectNodes("//Attr[@name='Title']");

        foreach(XmlElement node in nodes)

        {

            node.SetAttribute("value", "bar");

        }

        Console.WriteLine(xmlDoc.OuterXml);

    }

}