Changing Apple ID to install Software

When you first get your Macbook, they ask you to enter an Apple ID (The part where they ask you what language, time zone, etc), I had put my sisters account. Now that I actually have one, every time I go to update the latest software it automatically asks for her password which I do NOT have. It does not give me the option to remove her email. It seems that my account now is on as a secondary account to purchase aps and what not to all my devices. How do I put my apple ID as the primary account for the APP store on my Mac?

Thanks!