As a current Avast user I ask this question:
Is it better to download the new version, 4.7.817, unistall the old, and then install the new, or, use the “Program Update” feature?
The program update feature will work great. No problem.
You don’t have to uninstall, download, install again… lose your settings.
Just the automatic update and boot 
Thank you for your prompt reply. I thought this was the case, but wished to make sure.
No problem! 8)
The forum is here to this: help and learning 