Apple TV 4K
Selecting picture resolution
By default, your set-top box is set to the highest possible picture resolution. If you experience a slow connection or your TV doesn't support the highest picture resolution, choosing a lower resolution may help.
Highlight Settings.
Press the Centre key.
Highlight Video and Audio.
Press the Centre key.
Highlight Format.
Press the Centre key.
Highlight the required setting.
Press the Centre key.
Press and hold MENU to return to the main menu.