Changing UI Text to the Quality Level

Hey Guys, I wanted to make a main menu and have the quality settings work by pushing a button and changing the quality level up or down. I manage to work the changing of quality level but I cannot figure out how to make the text change to the Quality level. Here is my script:

 import UnityEngine.UI;
 
 var qualityText : Transform;
 var qualityLevel = QualitySettings.GetQualityLevel ();
  
 function Start(){
     
 }
  
 function Update () {
     qualityText.text = "" + qualityLevel;
 }
  
 function Increase()
 {
     QualitySettings.IncreaseLevel(true);
 }
  
 function Decrease()
 {
     QualitySettings.DecreaseLevel(true);
 }

And here are the errors:

 GetQualityLevel can only be called from the main thread.
 Constructors and field initializers will be executed from the loading thread when loading a scene.
 Don't use this function in the constructor or field initializers, instead move initialization code to the Awake or Start function.

 ArgumentException: GetQualityLevel can only be called from the main thread.
 Constructors and field initializers will be executed from the loading thread when loading a scene.
 Don't use this function in the constructor or field initializers, instead move initialization code to the Awake or Start function.
 QualityManager..ctor () (at Assets/EasyMenu/Resources/Scripts/QualityManager.js:4)