Resolution belongs to the viewing edition
HD, 1080p and 4K describe video formats, not the quality of a catalog poster. Open the available edition and check the service's format information. Device support, plan and connection can affect the choice. A title's appearance in the catalog does not establish that every format is available everywhere.
Steady playback before the highest number
If the image repeatedly stops, lower the quality setting where the player allows it. Adaptive playback may already adjust the picture as the connection changes. Give it a short chance to settle. A stable film with clear dialogue is usually more enjoyable than a high-resolution setting that keeps interrupting the story.
Phone, laptop or television?
A smaller screen may not benefit enough from the highest format to justify the extra data. On a suitable large television, a good higher-resolution edition can reveal more detail. Preserve the picture's aspect ratio and start with a sensible display preset rather than stretching or sharpening every movie.
Sound deserves a separate check
Look for dialogue enhancement or a night mode if your equipment offers one and speech is difficult to hear. Check subtitle size from your actual seating distance. If the sound arrives late, investigate the audio connection rather than repeatedly changing video resolution. The playback help page provides the next steps.