First there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac. This user tip describes what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community
That being said download and run the shareware app Find Any File to search for any files with the application's or the developer's name in the file name. For the AVG software you'd do the following search(es):
1 - Name contains avg
2 - Name contains avast
Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.
FAF can search areas that Spotlight can't like invisible folders, system folders and packages.
If you can't delete the files because you get a message that they are in use or something similar then boot into Safe Mode according to Start up your Mac in safe mode - Apple Support, run FAF and try deleting from there.
NOTE: Safe Mode boot can take up to 10 minutes as it's doing the following;
• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files