AVG Tuneup Unlimited

I have been a registered user for many years - well before AVG were involved.  I have Tuneup unlimited installed and have a lot of my family members linked to my Account.  My subscription is about to expire and one of my sisters says she is buying the software (from a registered AVG partner - I have paid in the past).  I cannot see how I can update my subsciption with the "activation" code - my account only seems to have the option to pay by card of Paypal.
I don't want to start a separate subscription because this will probably mean setting up all my family members again - most a not technical and would meen I would have to do it for them - too onerous!
Can I update my subsciption with a code using a Retail purchase as I would like?

Hello David,
I understand that you need to register the activation code of your AVG TuneUp unlimited. Please register it as per the steps mentioned below:
1. Visit the Registration Page: https://www.avg.com/en-us/code .
2. Enter your activation code.
3. Click 'Log in here' and enter your AVG My Account email address and password.
4. Click Register and Activate. Then click on 'Renew now' button in the pop up you encounter.
Thank you.

Hello David,
I understand that you need to register the activation code of your AVG TuneUp unlimited. Please register it as per the steps mentioned below:
1. Visit the Registration Page: https://www.avg.com/en-us/code .
2. Enter your activation code.
3. Click 'Log in here' and enter your AVG My Account email address and password.
4. Click Register and Activate. Then click on 'Renew now' button in the pop up you encounter.
Thank you.