Tried Repair. Said Error processing packages. Pls use full update.
Used Full Update - Said error while changing the product config. BTW, am using paid version.
Which exact "full update" you used? If you have avast Pro, then the message was for you to download the Pro Trial (no the Free). The same for AIS: download AIS trial.
In any case, after the installation over your current one,
reboot.
It is also not clear to me what you meant with "changing the product config". In any case, as I said, you install first the same edition of avast that you currently have, and reboot. Only after the reboot start changing settings or testing the results.
If you have not uninstalled avast yet, then you shouldn't need to care for the license (at least not for now).