Music Manager singleton change song

I have an Music Manager in my main menu scene that is a singleton. The reason for the singleton is that I wan't to play some songs through different scenes. So far so good...

But from the Music Manager I would also like to load different songs on specific scenes. So if a specific scene gets loaded the song should change.

How would I do this from within the Music Manager which is a singleton?

I tried it with checking which scene is loaded at that present moment but I can't seem to figure out how to properly do this. Any suggestions are welcome.

This is the code I tried for the Music manager:

 using UnityEngine;
 using System.Collections;
 using UnityEngine.SceneManagement;
 
 public class MusicManager : MonoBehaviour {
 
 
     public static MusicManager instance;
 
     // Vars for audio
     private AudioSource audioSource;
     public AudioClip MainMenuSongAU;
     public AudioClip GreenHillsSongAU;
     public AudioClip CaveSongAU;
 
     private bool SongLoaded;
 
     // Vars for checking which scene has been loaded at present moment
     private string lastScene;
     private string currentScene;
 
 
 
     void Awake () {
     
         MakeSingleton ();
 
         audioSource = GetComponent<AudioSource> ();
 
         //Getting the scenename
         lastScene = SceneManager.GetActiveScene().name;
 
     
 
         // Setting the music state standard to 1 so music starts playing on game load
         if(!PlayerPrefs.HasKey ("Game Initialized")) {
             MusicState.SetMusicState (1);
 
             PlayerPrefs.SetInt(" Game Initialized", 123);
         }
     
     
     }
 
 
     void Update() {
 
         // Checking which scene is loaded (for handling music)
 
         currentScene = SceneManager.GetActiveScene().name;
 
             if(currentScene != lastScene) {
             lastScene = currentScene;
             ChangeSong();
         }
 
     }
 
     // Changing the song when loading a specific level
     void ChangeSong() {
 
 
         if (lastScene == "GameStartInfo") {
             audioSource.PlayOneShot(GreenHillsSongAU, 0.4f);
 
             Debug.Log ("Var lastScene is now: " + lastScene);
         }
     }
 
 
 
 
 
 
     void MakeSingleton () {
     
         if (instance != null) {
             Destroy (gameObject);
         } else {
             instance = this;
             DontDestroyOnLoad (gameObject);
         }
     }
 
 
     public void PlayMusic (bool play) {
 
     
         if (play) {
             if (!audioSource.isPlaying) {
                 //audioSource.Play();
                 audioSource.PlayOneShot(MainMenuSongAU, 0.4f);
                 audioSource.loop = true;
             } 
         } else {
             if (audioSource.isPlaying) {
             }
             audioSource.Stop ();
         }
 
 
     }
 }

And this is the code for the Menu Controller and a music On/Off button that activates a function inside the Music Manager (MusicState and PlayMusic():

 using UnityEngine;
 using System.Collections;
 using UnityEngine.SceneManagement;
 using UnityEngine.UI;
 
 
 public class MainMenuController : MonoBehaviour {
 
 
     [SerializeField]
     private Button musicButton;
 
     [SerializeField]
     private Sprite[] musicIcons;
 
 
     private Text highScoreMainText;
 
 
 
     void Awake ()
     {
 
 
         highScoreMainText = GameObject.Find("HighScoreTextAmountMain").GetComponent<Text> ();
 
         SetHighMain ();
 
     }
 
     void Start () {
 
         CheckToPlayTheMusic ();
 
     }
 
 
 
     public void PlayGame ()
     {
         
         SceneManager.LoadScene ("GameStartInfo");
 
     }
 
 
     public void SetHighMain ()
     {
         int score = PlayerPrefs.GetInt("HighScore");
         highScoreMainText.text = "" + score;
     }
 
 
 
     void CheckToPlayTheMusic () {
         if (MusicState.GetMusicState () == 1) {
             MusicManager.instance.PlayMusic (true);
             musicButton.image.sprite = musicIcons [0];
         } else {
             MusicManager.instance.PlayMusic (false);
             musicButton.image.sprite = musicIcons [1];
             }
         }
 
     public void MusicButton () {
         if (MusicState.GetMusicState () == 0) {
             MusicState.SetMusicState (1);
             MusicManager.instance.PlayMusic (true);
             musicButton.image.sprite = musicIcons [0];
         } else if (MusicState.GetMusicState () == 1) {
             MusicState.SetMusicState (0);
             MusicManager.instance.PlayMusic (false);
             musicButton.image.sprite = musicIcons [1];
         }
     }
 
     }