To uninstall Avast Free Antivirus from a Windows computer, first disable the Self-Defense mode by opening Avast, clicking on Menu, selecting Settings, choosing General, then Troubleshooting, and unchecking the box next to Enable Self-Defense. Confirm the change by clicking OK. Next, open the Control Panel, select Programs and Features, find Avast Free Antivirus, click Uninstall, confirm by selecting Uninstall again, and then click Yes in the confirmation window. The uninstallation process will begin and may take some time. After completion, restart the computer to finalize the uninstallation.