Unity script doesn't work and complains about void Update, what's the problem?

Question

C++ / C#

I bought a textbook and follow it line by line.
I write the specified code, everything is according to the book. But it throws error
CS8025 C# Feature is not available in C# 4. Please use language version 7.0 or greater.
What am I doing wrong ?

The code itself

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class HelloWorld : MonoBehaviour {

  // Use this for initialization
  void Start () {
        //print("Hello World");
    
        void Update ()  {
            print("Hello World");
        }
  }
  
  // Update is called once per frame
  void Update () {
    
  }
}

Answer 1

Download the installer HERE .
There you select the items, as in the screenshot and install.