G’day and welcome to Avast forum.
Are you looking for this section see link http://www.avast.com/registration-free-antivirus.php
Edit: Their are two ways to do this to get a Avast free license using the free version see link
https://support.avast.com/index.php?languageid=1&group=eng&_m=knowledgebase&_a=viewarticle&kbarticleid=612