using System;

using System.Linq;

using System.Xml;

using System.Xml.Linq;

using System.Xml.XPath;

​

public class Program

{

    public static void Main()

    {

        var doc = XDocument.Parse(XmlString);

        var namespaceManager = new XmlNamespaceManager(new NameTable());

        namespaceManager.AddNamespace("xsi", "http://www.w3.org/2001/XMLSchema-instance");

        var names = doc.XPathSelectElements(

            "/MainClass/Items/Settings[@xsi:type='FileModel']/Name",

            namespaceManager

        ).Select(e => e.Value);

        Console.WriteLine(String.Join(", ", names));

    }

    private static string XmlString = @"<?xml version=""1.0""?>

<MainClass xmlns:xsi=""http://www.w3.org/2001/XMLSchema-instance"" xmlns:xsd=""http://www.w3.org/2001/XMLSchema"">

  <Items>

    <Settings xsi:type=""FileModel"">

      <Name>Rep1</Name>

      <IsActive>true</IsActive>

      <IsHidden>false</IsHidden>

    </Settings>

    <Settings xsi:type=""FileModel"">

      <Name>Rep2</Name>

      <IsActive>true</IsActive>

      <IsHidden>false</IsHidden>

    </Settings> 

   <Settings xsi:type=""ServerModel"">

      <Name>DelRep</Name>

      <IsActive>false</IsActive>

      <IsHidden>false</IsHidden>

    </Settings>

  </Items>

</MainClass>";

}