Avast Free Antivirus can be used free of charge at home and for non-commercial use. It is no longer necessary to register your Avast Free Antivirus, as your initial free subscription automatically activates after installation. When your free subscription expires, you can let the program automatically re-subscribe itself.
Alternatively, you can manually activate your 1-year free subscription:
Open the Avast program and click on "Menu" at the top left hand side.
On the My Subscriptions screen in Avast Free Antivirus, click Upgrade Now next to Avast Free Antivirus in the list located under Subscription on this PC.
Click Select in the Avast Free Antivirus column.
Click the X in the top-right corner of the upgrade screen that appears to return to the My Subscriptions screen.
Your Avast Free Antivirus subscription is now activated for one year. The expiration date of your subscription appears under Subscription on this PC.
For details, refer to the following article: