There was indeed an easy way to go from Paid to Free in version 2015.
I have no idea why Avast decided to replace something that made it easy to keep customers
with a survey???
Now, in order to change from Paid to Free, you need to download the Free Version then, use the control panel Removal feature.
Reboot your system.
Once that's dome you can run the setup program for the Free version of Avast.
What a Pain......