First of all, nice AV folks. For what it’s worth, I recommend it to all my friends.
Unfortunately, my machine is a few years old. I have Avast set to scan all files on access and to scan all files + archives + through option on manual scans.
How should I set Avast to keep my pc safe but to also optimize my pc performance.
Thanks in advance. 
Just keep the sliders to Normal Sensitivity and optionally disable Scan on move/copy.
This should keep virtually the same protection with lowest drag.
You could also disable archive scanning, which (especially on some systems) could save a lot of time. The contents of archives can’t do any harm till they’re expanded, one way or another, and opened, at which point Standard Shield will catch harmful ones anyway. So that’s probably a quite reasonable speed-vs.-safety tradeoff.
Thank for the suggestions.
S.R.