product change for family member from N360 to N.S.

Another family member uses Norton 360 on tower format computer, and the subscription expires in a month.  The other user has poor internet & online registration skills and has simply been accepting whatever automatic renewal that occurs, but  now the goal is to put on a Norton Security install.  Not sure is what will happen for the money or credit.  

Download and Install NS from the "...latest/ns" direct link, buy a license key from a retail store, do the registration information when the product reaches that stage in the installation process

OR

Download the NS from "...latest/ns" direct link, completely uninstall and remove N360, INSTALL the new Norton Security, and will the current "registered" user's current account pickup the registration fee-or-charge on its own without interrupting the registration process

OR

What?  Something else?

The accounts for myself and the other users are two separate ones.  I know mostly what to do for MY OWN account, but the other family member has the separate account both online and in financing the registration.  I would like to avoid spending cash green money for a new NS license registration key because auto-renewal is already setup.  If I spend the cash for the other user's license fee,  then I would not want auto-renewal to confuse the situation.  Not know if auto-renewal is smart enough to know to act or not.  I myself hope to let the user keep the same expiration date with the only change being removal of Norton 360 and putting in Norton Security.

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Affected Machine:  64-bit, Windows 10, tower shaped computer, 11 months old