speaking about Apple ID: how do you change it???

[Gilbert]

It's fairly easy. You log into your account at appleid.apple.com, click on the "Edit" button on the right in the "Account" section, scroll down to the "Reachable At" section and click "Add More". You then add your new address that you want to use. Once it is confirmed, you can go back back toe "Edit" section and select "Change Apple ID..." and you can then select from all of your confirmed email addresses.

Here is the full write-up from Apple:

https://support.apple.com/en-us/HT202667

Good luck!

EDIT: You may have to re-authorize all the devices if you choose to remove the old email address. You can keep it on the account as I don't think it affects anything.