Go to Settings → General → Screen Saver You can then select how often you want to download new screensavers, and which you want.
It is also possible to set up a screensaver with your own photos from iCloud.
How to Customize the screen saver on your Apple TV
NEXT TIP
How to Customize the subtitles on your Apple TV
Go to Settings → Accessibility → Subtitles and Captioning → Style You can then select a larger size, or click on «Edit Styles» and customize every aspect of your subtitles.
TIP FROM
8 Apple TV Tips and Settings
How to customize Apple TV remote, pair AirPods, calibrate display, and set up screensavers