Changing old Apple ID in AppStore function

I inherited my iMac from a family member,

Each Apple device is linked/associated with an Apple ID of the person who did the setup, in your case a family member.

Activation Lock is designed to prevent others from using your Mac if it's lost or stolen.

To unlock the iMac, you need the Apple ID and password of the previous owner, that were used during set up.

The previous owner has to read -> What to do before you sell, give away, or trade in your Mac

What to do before you sell, give away, or trade in your Mac - Apple Support

Then the previous owner has to remove the iMac from his account, see this Apple article:

Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to see where you're signed in - Apple Support

Then you can sign in with own your Apple ID.

See -> Activation Lock for Mac -> Activation Lock for Mac - Apple Support

👉 How to disable Activation Lock

To disable Activation Lock, turn off Find My:

1. Choose Apple menu  > System Preferences, then click Apple ID.
2. Select iCloud in the sidebar, then deselect Find My Mac on the right.
3. Find My also turns off when you sign out of iCloud, such as when preparing to sell, give away, or trade in your Mac.

If you don't have access to your Mac, use a web browser on another device to remove Activation Lock.

If your previously owned Mac shows an Activation Lock window that asks for someone else's Apple ID, the previous owner may need to remove Activation Lock for you.

You can also contact Apple support for help, -> Get Support (apple.com)

You have to show proof of ownership of your product, provide all documentation showing your purchase of the device.

If you do not have additional proof of ownership, contact the reseller. They may be able to provide the original purchase document.

Once Apple receive your proof of ownership, Apple will further review your request and provide an update.

Delete and redownload the applications you're trying to update. The old Apple ID is stored inside them.

On a Mac, this won't affect their documents, but those should be backed up anyway.

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