How can I change my account but keep everything else?

My sister and I have always shared an itunes account so we don't have to pay twice for everything (ex: music and games that cost money). But now, my sister will be leaving for college, and I have to start to create my own account, otherwise I won't be able to update my apple products. If I change the itune account on my ipad, is there a way to keep all of my pictures and videos safe? Also, will I have to use a new gamecenter account that corresponds to my new apple ID as well?