Mac update

Are you logged in as a user with admin privileges?

What, exactly, is the error message displayed when the update fails?

You might try starting you Mac in Safe mode and trying to install the update while booted that way.

How to use safe mode on your Mac - Apple Support 

Safe mode can very often correct weird software behavior by forcing the OS to do cache clearing and other housekeeping. When you're in safe boot, the machine will not be at its best performance, especially with graphics, but that's expected.

Does the problem persist while in Safe mode?

Exit safe mode by restarting your Mac normally and re-evaluate the issue again.

saahene Said:

"Mac update: when i try to update my laptop it says i need to be the owner of the laptop hence update failed. why is this happening?"

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Troubleshooting Failed Mac Update:

Is this a Used Mac?

If so, and you cannot sign in, then you need to have the person currently signed in to iCloud on it sign out on iCloud. Once they signed out, your need to restart the device, and then sign yourself in. Elsewise, it is useless to you. Go to: System Preferences, and click the name on the top left.

Have the Current Person Use this Site: What to do Before you Sell, Give Away, or Trade in your Mac - Apple Support

Learn from this:

So, contact them, seeing if this can be done. If this is on no option, then take this as a learning experience, knowing to always be allowed to log into it prior to purchasing a used Mac.