using System;

using HtmlAgilityPack;

using System.Linq;

using System.Xml;

public class Program

{

    public static void Main()

    {

            HtmlDocument doc = new HtmlDocument();

            doc.LoadHtml("<BIG><BIG><BIG>Text</BIG></BIG></BIG>");

​

            var result = doc.DocumentNode.Descendants("BIG").FirstOrDefault();

​

            if(result != null)

            {

                doc.DocumentNode.RemoveChild(result, true);

            }

​

            Console.WriteLine(doc.DocumentNode.OuterHtml.ToString());

​

    }

}