Why is Apple and iTunes so complicated

I've had my own Iphone for about two years now and its still under my moms account and debit card who also has an iPod. How can I change the e-mail.Apple ID.debit card info. And iTunes and my e-mail login for JUST my device? Is this posible I've been trying to figure it out for like a year.

Go to settings<AppStore then click apple Id and log out