19 to 20, you might want to go over favourites a bit, as they are more prominent and easier to manage in 20. Replace the 19 libraries with the 20 libraries and that would pretty much be it. I haven't worked with 20 much, yet, we only got it here in NL last week, but I don't think there are massive overhauls to attributes (like building materials, or cinerender) that would make it a big change.