Pavel Popchikovsky

Пример из документации к QualitySettings.SetQualityLevel()

using UnityEngine;
using System.Collections;

public class ExampleClass : 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();
    }
}

Адаптируйте под себя.