Screen.SetResolution  

static function SetResolution (width : int, height : int, fullscreen : boolean, preferredRefreshRate : int = 0) : void

Description

Switches the screen resolution.

A width by height resolution will be used. If no matching resolution is supported, the closest one will be used.

If preferredRefreshRate is 0 (default) Unity will switch to the highest refresh rate supported by the monitor.
If preferredRefreshRate is not 0 Unity will use it if the monitor supports it, otherwise will choose the highest supported one.

In the web player you may only switch resolutions after the user has clicked on the content. The recommended way of doing it is to switch resolutions only when the user clicks on a designated button.

A resolution switch does not happen immediately; it will actually happen when the current frame is finished.

// Switch to 640 x 480 fullscreen

Screen.SetResolution (640, 480, true);

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        Screen.SetResolution(640, 480, true);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        Screen.SetResolution(640, 480, true)

Another Example:

// Switch to 640 x 480 fullscreen at 60 hz

Screen.SetResolution (640, 480, true, 60);

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        Screen.SetResolution(640, 480, true, 60);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        Screen.SetResolution(640, 480, true, 60)

Another Example:

// Switch to 800 x 600 windowed

Screen.SetResolution (800, 600, false);

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    void Example() {
        Screen.SetResolution(800, 600, false);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    def Example():
        Screen.SetResolution(800, 600, false)