how do i delete a previous owners information off of my mac book pro so i stop getting her updates?

When I purchased my mac book pro I got a discount off of it because it was an open box- I didn't realize it meant that there was a previous owner. Her information is still on my macbook somewhere and I do not know how to delete it! I have updates for her email address for certain apps like iPhoto which I cannot even access now because it needs to be updated- but i cannot update it because the update is for the previous owners account! Please help me!!