Q: Serial number for a mac book pro

1.  What does a serial number have to do witn anything?

2.  What app are you talking about that tells you there is an upgrade

are you the first  and only authorized account on your macbook pro? did you or family or firends have a different email account that the app is tied to?

...i have an ipad from generation one. it was a gift and my cousin installed a few games, but it's linked to his account. everytime i need to update i will need to login with his account otherwise it's locked...

Assuming you're talking about the App Store... you still have clarified that...then have you tried signing out of it and sign back in using your own credentials?