is it possible for me as a foreigner to do all my studies in spain not only for a half year?

Your best option is always to begin with your Embassy. If you're still in Spain, go to your own country's embassy; if you're back at home, go to the Spanish Embassy. Many students study abroad every year, so they will know about it. If you are a known visitor, it is always possible that you can get a different Visa and remain as a student. But I can tell you, from experience, that usually they tell you that you must leave on the old Visa and come back on the new one; ridiculous as that is.

Good luck!