function OnGUI ()
{
    var names = QualitySettings.names;
    GUILayout.BeginVertical ();
    for (var i = 0; i < names.Length; i++)
    {
        if (GUILayout.Button (names[i]))
            QualitySettings.SetQualityLevel (i, true);
    }
    GUILayout.EndVertical ();
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void OnGUI() {
        string[] names = QualitySettings.names;
        GUILayout.BeginVertical();
        int i = 0;
        while (i < names.Length) {
            if (GUILayout.Button(names[i]))
                QualitySettings.SetQualityLevel(i, true);
            
            i++;
        }
        GUILayout.EndVertical();
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def OnGUI():
        names as (string) = QualitySettings.names
        GUILayout.BeginVertical()
        i as int = 0
        while i < names.Length:
            if GUILayout.Button(names[i]):
                QualitySettings.SetQualityLevel(i, true)
            i++
        GUILayout.EndVertical()