How do I authorize my computer in Windows 10?
There is option to download my purchased music, but when I do, it says computer is not authorized. There is a page where I can De-authrorize, but not authorize
It's done via the Store drop-down menu at the top of iTunes - if the drop-down menus aren't showing then try control-B
e.g. (this screenshot is from a Mac but it should be similar on a PC)