Apple Monitors: How To Change Resolution
1. Select the Monitors control panel from the Apple menu, it may also be called Monitors and Sound.
Note: If you have more that one monitor, a separate Monitors control panel will appear on each display.
2. Click on the resolution you desire in the Resolution section of the control panel.
3. The new resolution will be displayed after you select it.
4. Close the Monitors control panel by clicking the close box in the upper-left corner.
5. If the image is distorted, adjust the video controls in the Monitors control panel or on the monitor itself.