When you install Avast, it prompts you to register for free to enjoy protection for 1 year. When this period expires, the software prompts you to renew your license by redirecting you to the retail version of the product. But you can completely renew your free license.
How to renew your Avast license for free
When Avast displays an alert about the expiration of your license, click the button Renew your license now.
In the table that appears, click the Choose gray button, in the column Basic protection.
Enter your name and email address and click on the button Register to get the free license.
Avast is once again trying to upgrade to the premium paid version. Close the window to decline.
You have successfully registered again for 1 year with the free antivirus.