How can I have 4K capability added to my existing Apple TV service

Apple TV Plus content is produced in 4K, and all iTunes purchases will show whether they are available in 4K. There is nothing to add, it will always stream at the highest quality. If you bill other services through your account you will need to refer to their service as to support of 4K. Now in order to ensure it is streaming at that quality, it will be dependent on your connection and equipment (i.e. internet connection of at least 25mbps, 4K capable display, high speed HDMI cable)

You will need

• 4K input and processing (Apple TV 4K),
• a 4K (TV) screen,
• and of course 4K content (e.g. a movie).