I have a late 2013 rMBP that shipped with 10.9 and I never updated it when 10.10 came out. I've continued to ride 10.9 because it works perfectly and I really like the classic OS X look versus the new style they started with in 10.10. However, it's starting to become annoying being so many releases behind and I've decided to upgrade to 10.12. Can I just click the upgrade button in the Mac App Store or do I need to do something special because I'm on such an old operating system? The Mac App Store bothers me roughly once per month to upgrade but I don't want it to get botched and be a big hassle. I know to back up all my data before doing the upgrade.