Where to start to study astronomy in the future?Watch
If you meant what you can do at university, there's quite a choice. I recommend you have a look around on www.search.ucas.com. Depending on your other scientific interests, you may want to enter terms like 'astronomy', 'astronomy & physics', 'astrophysics' and so on.
Edit: As Plagioclase has said, you'll probably you'll also need to primarily take physical sciences at A Level to get into the kind of course you want to get into.