Read the edition, not the poster
Movie artwork is designed to look sharp. It does not establish the resolution of a stream. Use the viewing service's edition and player settings to check HD, 1080p or 4K availability. The device, plan and connection can affect what the player offers even when a higher-quality version exists elsewhere.
Stability matters too
If a higher setting repeatedly pauses, try a lower available quality and let it settle. A consistent picture can be more enjoyable than frequent interruptions. Check for other heavy network use before changing several device settings at once. An automatic setting may adjust the picture as conditions change.
A dark film and bright animation should not necessarily look alike. Grain, shadow and color are parts of the source as well as the display. Avoid stretching the frame merely to remove empty edges. If the entire image looks wrong, confirm the television's selected mode and the service's help before assuming the movie file is faulty.
Finish with sound and captions
Picture quality is only part of a comfortable watch. Select the right audio output, subtitle language and text size where supported. Check those settings early in the film so that the rest of the evening can be about the story rather than repeated adjustments.