Why would AA give you a complimentary upgrade?

Sometimes, you might receive what's called an "op up" or operational upgrade. There's a very long thread on this forum devoted to that discussion (you can find it through the search feature).

But in most cases, the chances are pretty slim.

This link might also help you understand AA's upgrade procedures. It's from the FAQ at the top of the page, where it says, "Please check here first!"

How can I upgrade on AA?