using System;

using System.Linq;

using System.Xml.Linq;

​

public class Program

{

    public static void Main()

    {

        const string xml = @"<?xml version=""1.0"" encoding=""utf-8""?>

                             <Main version=""1.0"" xmlns=""urn:root:v1"">

                                 <Report>

                                     <Title>Some Value</Title>

                                 </Report>

                                 <Content>

                                     <Address>

                                         <CountryName xmlns=""urn:location:v2"">Australia</CountryName>

                                     </Address>

                                 </Content>

                             </Main>";

​

        var doc = XDocument.Parse(xml);

​

        doc.Descendants().Attributes().Where(x => x.IsNamespaceDeclaration).Remove();

        doc.Root.Add(new XAttribute(XNamespace.Xmlns + "root", "urn:root:v1"));

        doc.Root.Add(new XAttribute(XNamespace.Xmlns + "loc", "urn:location:v2"));

​

        Console.WriteLine(doc);

    }

}