Make a fade in/out inside 'upDate()' function

I'm new using Unity, and I want to make a fade in/out to my loading screen scene I've made. My code is the following:

 // Use this for initialization
     void Start () {
 
     }
     
     // Update is called once per frame
     void Update () {
         if (loadedScene == false) {
             loadedScene = true;
             StartCoroutine( HandleIt() );
             StartCoroutine (LoadNewScene ());
         } else {
             FadeIn ();
             if (currentAmount < 100) {
                 currentAmount += speed * Time.deltaTime;
                 TextIndicator.GetComponent<Text>().text = ((int)currentAmount).ToString () + "%";
 
             } else {
                 TextIndicator.gameObject.SetActive (false);
                 complete = true;
                 FadeOut ();
             }
 
             progressBar.GetComponent<Image>().fillAmount = currentAmount / 100;
         }
     }
 
     // The coroutine runs on its own at the same time as Update() and takes an integer indicating which scene to load.
     IEnumerator LoadNewScene() {
 
         while (complete == false) {
             // This line waits for 3 seconds before executing the next line in the coroutine.
             // This line is only necessary for this demo. The scenes are so simple that they load too fast to read the "Loading..." text.
             yield return new WaitForSeconds(1);
         }
 
         yield return new WaitForSeconds(0.5f);
 
         // Start an asynchronous operation to load the scene that was passed to the LoadNewScene coroutine.
         AsyncOperation async = SceneManager.LoadSceneAsync(2);
 
         // While the asynchronous operation to load the new scene is not yet complete, continue waiting until it's done.
         while (!async.isDone) {
             yield return null;
         }
 
     }
 
     void FadeOut() {
         
         fadeOverlay.CrossFadeAlpha(1, 0.4f, false);
     }
 
     /* I guess this starts the Fade Image at the beginning...xD */
     void FadeIn() {
         fadeOverlay.CrossFadeAlpha(0, 0.3f, true);
     }
 
     private IEnumerator HandleIt()
     {
         FadeIn ();
         yield return new WaitForSeconds( 0.3f );
     }

As you can see I try different things for the fade in and for the fade out, but none works...when I run it I see no fade in/out at all...So, can anyone help me? I'd be very grateful!