I used to use an old email address for my apple id but changed the email for my apple id a year ago. Whenever I update my computer, it brings up my old email as my apple id and wants me to put in my old PW which I don't remember. Why?

Thanks for your reply! I think I didn't use the correct terminology in my post. When I changed my Apple ID email, I did it while I was on the phone with Apple support so they could help me. The guy I talked to there said (I think) that I would have to keep one of the emails that I had originally signed up with (I had my old email and then my backup email I guess.) He said we could use my backup email for the main email and make a new password which I did. So does that change your reply to me at all about why my old email keeps showing up when I restart my computer saying that I need to update my password for that old email for iCloud?? Thanks for your help!

If I go and open up System Preferences and then iCloud, it has my new/correct email and lets me put in my password. I didn't see my old email anywhere. But when my computer restarts/updates/ and sometimes I think for reasons I'm unaware of, it has that system preferences/iCloud window open asking for me to update the password for my old email. I did try to enter my new password into that old email and it says it's not correct.

I didn't do a name change, but I did read the article you referenced. It said you need to sign out of all of your Apple services first - I don't remember doing that but I did have an Apple support person on the line telling me what to do when I wanted to change emails associated with my Apple ID so?????