using System;

using Newtonsoft.Json;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        var json = "{\"title\" : { \"newTitle\" : \"Test\"}, \"tags\" : { \"newTags\" : [\"Tag1\", \"Tag2\"] }}";

        var inputObj = JsonConvert.DeserializeObject<JsonInput>(json);

        inputObj.Title.NewTitle = "Test2";

        inputObj.Tags.NewTags = new string[] {"TagA", "TagB", "TagC"};

        Console.WriteLine(JsonConvert.SerializeObject(inputObj));

    }

}

​

public class JsonInput

{

    public Title Title {get;set;}

    public Tags Tags{get;set;}

}

​

public class Title

{

    public string NewTitle {get;set;}

}

​

public class Tags

{

    public string[] NewTags {get;set;}

}