Cannot do updates because I can't change Apple ID
I am trying to do Updates in the Apps Store on my MacBook Air and the wrong (an old one) Apple ID keeps appearing in the Apple ID box. I have signed in and out of the Store and it keeps appearing and won't let me change it. I cannot delete the App Store app as computer won't allow me to do this and when I try I get a message saying I cannot delete as it is required by OS X. Can someone help with this please.
MacBook Air 13″, OS X 10.10