Problem with Avast Internet Security

Helllo!

My problem is that my 30-trials days are now done but I can’t go back to Avast Free. It doesn’t appear the go back to Free Avast option in the subscribtion tab. How can I go back to the other versión of Avast?

Thanks!

See: https://www.avast.com/faq.php?article=AVKB12#idt_02