How to break up with my gf during winter vacation?

I've been dating this girl for a few months now, and I've decided to break up with her. The problem is, we sit very close to each other in one of our classes and we both have good relationships the other kids around us, it is also Christmas time so I don't want to ruin a Christmas.

How can I break up with her so I can start a relationship with the girl I really want to spend Christmas with? I'm ok with staying friends with her, I just don't want to make things unbearably awkward.

Also final exams start the week after we get back from break so I don't want to hurt her grade for any reason.