Google Play will upgrade your HD movies to 4K for free
 

If you purchased a movie in SD or HD from Google Play in the past, make sure to fire up the Movies & TV app as soon as you can. Google will tell you if your previous purchases are now available in 4K, and if they are, you can get the upgrade at n...

https://www.engadget.com/2018/10/23/...ee-4k-upgrade/