I made a mistake and tried the ‘AVAST Internet Security trial’ version on two machines and now they have no protection after the trial period expired.
Please, tell me how to switch back to AVAST FREE or do I need to reinstall as my only option?
Thank you!
Culinor welcome to Avast! forums.
Open Avast! > MAINTANANCE > Subscription > Switch back to AVAST FREE
https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=1219#idt_02
thank you, that was fast
appreciate it
avast is cool
You are welcome 
OK, how do we do that in 2019 now?
FAQ >> https://support.avast.com/
It would probably have been better to create your own new topic, as much has changed, rather than resurrect a very, very old topic.
You don’t say what it is that you want to switch back from ?
If is is Avast Internet Security trial, this isn’t too difficult go to Control Panel, Programs & Features, Uninstall Avast Antivirus, this should give the option to go back to Avast Free.
However, if this is a 60 day Trial version ?
Much has change as you would have needed to give payment instructions so payment can be made at the end of the trial. This mandate would also need to be cancelled or payment would be made, even though went back to Avast free.