Hello ms_wiggles,
Thanks for that info and for choosing the Apple Support Communities. If I understand correctly, you are unable to sign out of an old Apple ID in the iTunes app on your Mac. To do this, please follow these steps from this Apple resource:
"After you set up an Apple ID, you can sign in to the iTunes Store to buy music and video, view or change your account information, and see your purchase history.
When you finish using the store, you can sign out to prevent anyone else who has access to your computer from making purchases using your account.
- In the iTunes app
on your Mac, choose Account > Sign In (or Sign Out)."
Set up and manage an iTunes Store account on Mac
Cheers!