Change the default video format in the Apple TV app
If you have a slow internet connection or want to use less data, you can choose to limit all purchases and rentals to the standard-definition (SD) format in the Apple TV app. If you want better quality high-definition (HD) videos, turn this setting off.
Limit purchases and rentals to SD
In the Apple TV app , navigate to Settings.
Turn on Limit Purchases and Rentals to SD.