How to convert my itunes hd videos to 1080p

I have in the past bought many itunes movies and tv shows in HD(720p) format. Now that 1080P format is supported how so I convert my old 720p files easily to the higher definition 1080p version.

Just sign in again on iTunes, check your purchases, re-download the 1080p version as I understand it.

I'd try chas' method first. Im not familiar with iTunes' video, but I'd be surprised if they didn't allow that.

But I'll chip in just to say that it is not possible to "convert" a lower resolution into a higher one. I heard a good saying once - "you cant magic extra pixels from nothing."

You can upscale - but thats just playing 720p on a 1080p screen.

Looks like certain movies have the sd, 720p and 1080p avalable. Will redownloading it download all three versions essentially taking up 10gigs of space per movie or will it replace the 720p version.