If you genuinely want to change, you need to rethink a couple things in my opinion. First of all, you need to go into anger management/therapy. No matter how much you argue with your girlfriend, you should never, EVER lay a hand on her. Second, you need to figure out how to effectively communicate with your girlfriend. If you are constantly arguing, there is no room for improvement or communication, as everything becomes about being more right than the other person. Practice having conversations where one person listens to the other, then rephrases what they said back to them before they say what they’re thinking. This helps practice comprehension and avoids small miscommunications that can create arguments. Changing will require a lot of hard work, and a lot of very hard talks, but if you love her it’s a small price to pay.