Here is an example to convert a C# class into a singleton pattern based System.Lazy:

using System;

namespace MyNamespace
{
    // 1. Make the class as a "public sealed"
    public sealed class MyClassName
    {
        // 2. Add these lines of code
        private static readonly Lazy<MyClassName> lazy = new Lazy<MyClassName>(() => new MyClassName());
        public static MyClassName Instance { get { return lazy.Value; } }

        // 3. Make the constructor as "private"
        private MyClassName() {}

        // 4. Example methods we want to expose
        public void MyFooFunction() {}
        public void MyBarFunction() {}
    }
}

Here is how we will use it:

using System;
using MyNamespace;

namespace ExampleProgram
{
    class Program
    {
        static void Main(string[] args)
        {
            MyClassName.Instance.MyFooFunction();
            MyClassName.Instance.MyBarFunction();
        }
    }
}