How do I download music videos from iTunes in HD?

I do not have an Apple Subscription. Instead I purchase my music videos from the iTunes Store and save them on my iMac. I have noticed that the music videos that I have previously downloaded are now available in higher quality HD versions. I nave two questions.

First, how do I replace the lower quality videos with the HD versions? Secondly, how do I make sure that my future downloads will be the HD quality versions?

Everything that I have found so far deals with changing preferences in the iTunes Store preferences, - which no longer exist. Any other tips would be appreciated.