Disabling Automatic Renewal service for Avast orders distributed by Nexway
https://www.avast.com/en-us/faq.php?article=AVKB136#artTitle

Disabling Automatic Renewal service for Avast orders distributed by Digital River
https://www.avast.com/en-us/faq.php?article=AVKB126#artTitle

Access help on this topic within the Avast User Interface:
https://forum.avast.com/index.php?topic=165749.msg1181311#msg1181311

How to cancel auto-renewal of my Avast License:
https://www.avast.com/faq.php?article=AVKB24#idt_010

You can also look at/change the auto-renewal yourself here: https://www.avast.com/find-order