Change apple ID on a computer
I was going to sell my mac mini to a friend, but the deal fell through.
I'm getting notices that there are updates available, but first it tries to log in on his account, then tells me that I can't update the software using my own apple ID. How do I change the system so that my Apple ID is the one associated with the computer?
Mac Pro, OS X El Capitan (10.11.5), Photos