Not needed for enlisted. Just see a AF recruiter and go be "Above All"

Only If you want to be a officer

You should decide what you want to do in the Air Force. If you want to do something specific (say–engineering) than you will need that degree. There are resources out there that tell you what jobs you will need a specific degree for. If you don't really care what you do in the AF than a get a degree in what you like.