按值传递引用类型 中间那句为什么赋值不对呢？

namespace 如何实现按值传递引用类型
{
    class Program
    {
        static void Main(string[] args)
        {
            //按值传递引用类型
            Console.WriteLine("输入用户年龄信息：");
            MyInfo ferd = new MyInfo("亭子", 22);
            Console.WriteLine("未按值传递引用类型前：");
            ferd.PrintInfo();
            SendAPersonByValue(ferd);
            Console.WriteLine("按值传递引用类型后：");
            ferd.PrintInfo();
            Console.ReadKey();
        }
        public static void SendAPersonByValue(MyInfo info)
        {
                //info.MyAge = 23;
                info = new MyInfo("小名",23);          //重新赋值
        }
    }

    class MyInfo
    {
        public string MyName;
        public int MyAge;
        public MyInfo(string name, int age)     //构造函数！（1.与类同名 2.没有返回值）
        {
            MyName = name;
            MyAge = age;
        }
        public MyInfo() { }
        public void PrintInfo()                //一般函数
        {
            Console.WriteLine("{0}年龄是{1}岁", MyName, MyAge);
        }
    }
}