As Tech asked, why don’t you want to update to v2014?

To “downgrade” to less protection…

  1. Download and save http://files.avast.com/iavs9x/avastclear.exe
  2. Download and save http://filehippo.com/download_avast_antivirus/15860/
  3. Run uninstaller from step #1 (you will be prompted to run in safe mode, do so)
  4. Reboot
  5. Install v8.0 from step #2
  6. Reboot
  7. Insert license key and reboot again.

edit: Before inserting license make sure the program auto-update is set to “manual”.