How to "Divorce" Macbook's original Apple ID? An MBA (Macbook Air) is configured with High-Sierra.  It was bought and configured with a relatives Apple ID.  I inherited the MBA: the iCloud account is set to my Apple ID. When trying install Apple updates, both Apple IDs do not work.  Why is this and what is the remedy?  

I would like my Apple ID to be authoritative to enable updates from Apple. What would need to be done?

Update: no apps are downloaded from the Apple store.
Apple covers this expertly. 


https://support.apple.com/en-us/HT201065


Once you have a backup, you can restore the documents and not the apps or restore the apps and delete only the ones with an embedded AppleID that’s wrong. 

With this procedure you don’t need any access to any AppleID or any previous passwords.