using System;

using Newtonsoft.Json.Linq;

public class Program

{

    public static void Main()

    {

        string json = @"

            {

              ""ResponseType"": ""VirtualBill"",

              ""Response"": {

                ""BillHeader"": {

                  ""BillId"": ""7134"",

                  ""DocumentId"": ""MN003_0522060"",

                  ""ConversionValue"": ""1.0000"",

                  ""BillType"": ""Vndr-Actual"",

                  ""AccountDescription"": ""0522060MMMDDYY"",

                  ""AccountLastChangeDate"": ""06/07/2016""

                }

              },

              ""Error"": null

            }";

        JObject jo = JObject.Parse(json);

        jo.Property("ResponseType").Remove();

        json = jo.ToString();

        Console.WriteLine(json);

    }

}

​