C# Accessing Quality Settings Preset Values

Here's a C# example of how to change the AA settings using a Horizontal Slider. Not too in depth, but should get you started.

 using UnityEngine;
 using System.Collections;
 
 public class Example : MonoBehaviour 
 {
     float aa = 0;
     
     void Update()
     {
         if(QualitySettings.antiAliasing != aa)
         {
             QualitySettings.antiAliasing = (int)aa;
             print (QualitySettings.antiAliasing);
         }
     }
     
     void OnGUI()
     {
         aa = GUI.HorizontalSlider(new Rect(0, 0, 256, 32), aa, 0, 8);    
     }
 }

Here's another example of how to change the actual quality preset. In this example I'll also use a Horizontal Slider.

 using UnityEngine;
 using System.Collections;
 
 public class Example : MonoBehaviour 
 {
     int level;
     string label;
     
     void Awake()
     {
         level = QualitySettings.GetQualityLevel();    
     }
     
     void Update()
     {
         if(QualitySettings.GetQualityLevel() != level)
         {
             QualitySettings.SetQualityLevel(level);
         }
         
         if(label != "Quality Level = "+QualitySettings.GetQualityLevel().ToString())
             label = "Quality Level = "+QualitySettings.GetQualityLevel().ToString();
     }
     
     void OnGUI()
     {
         level = (int)GUI.HorizontalSlider(new Rect(0, 0, 256, 32), level, 0, 5);
         GUI.Label(new Rect(0, 64, 256, 32), label);
     }
 }