>>You can determine your current version of Windows by running "winver" from the start menu or a CMD prompt. The Anniversary update reports "Version 1607" as the major version. I believe the most common prior major version is 1511.
>
>Yep, I've got 1511. I'm really not looking forward to this. Just to be safe I'm going to uninstall Start 10, the Start Menu replacement app.

No issues when upgrading to 1607 here - I had my machines do it while I was sleeping so I can't say how long it took.