using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        List<Product> oldList = new List<Product>();

        List<Product> newList = new List<Product>();

        oldList.Add(new Product(1, "ewrdsfads"));

        oldList.Add(new Product(2, "dsfdsfads"));

        oldList.Add(new Product(3, "addsfads"));

        Console.WriteLine("Before");

        oldList.ForEach(x => Console.WriteLine(x.id+" + "+x.url));

        newList.Add(new Product(2, "123456"));

        Console.WriteLine("");

        oldList = oldList.Select(ele =>{return (newList.Any(i => i.id == ele.id) ? newList.FirstOrDefault(newObj => newObj.id == ele.id) : ele);}).ToList();

        Console.WriteLine("After");

        oldList.ForEach(x => Console.WriteLine(x.id+" + "+x.url));

    }

}

​

public class Product

{

    public int id;

    public string url;

    public Product(int id, string url)

    {

        this.id = id;

        this.url = url;

    }

}