Screen.SetResolution

Description

Switches the screen resolution.

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

If preferredRefreshRate is 0 (default) Unity switches to the highest refresh rate that the monitor supports.
If preferredRefreshRate is not 0 Unity uses it if the monitor supports it, otherwise it chooses the highest supported one. Changing refresh rate is only supported when using exclusive full-screen mode.

On Android fullscreen controls the SYSTEM_UI_FLAG_LOW_PROFILE flag to View.setSystemUiVisibility.

To set a specific full-screen mode on a desktop platform, use the method overload that accepts the FullScreenMode parameter. Exclusive full-screen mode is only supported on Windows standalone player.

If you use multi-display, you can only use Screen.SetResolution to set the resolution of the primary screen.

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

using UnityEngine;

public class ExampleScript : MonoBehaviour
{
    void Start()
    {
        // Switch to 640 x 480 full-screen
        Screen.SetResolution(640, 480, true);
    }
}

Another example:

using UnityEngine;

public class ExampleScript : MonoBehaviour
{
    void Start()
    {
        // Switch to 640 x 480 full-screen at 60 hz
        Screen.SetResolution(640, 480, FullScreenMode.ExclusiveFullScreen, new RefreshRate() { numerator = 60, denominator = 1 });
    }
}

Another example:

using UnityEngine;

public class ExampleScript : MonoBehaviour
{
    void Start()
    {
        // Switch to 800 x 600 windowed
        Screen.SetResolution(800, 600, false);
    }
}

Additional resources: resolutions property.