The Avast Setup wizard enables you to modify Avast Antivirus.
To uninstall Avast Antivirus, refer to the following article:
Access the Avast Setup wizard
If you are using a trial version of a paid Avast Antivirus product or your paid license is close to expiration, you have the additional option to Switch Back to Avast Free Antivirus to convert your paid version of Avast Antivirus to Avast Free Antivirus.
- Right-click the Windows
Start button and select Apps and Features from the menu that appears. 
- Ensure that Apps & Features is selected in the left panel, then click your version of Avast Antivirus, and select Modify.
- Press the
WinXkey simultaneously, then select Programs and Features from the menu that appears.
- Right-click your version of Avast Antivirus, then select Change from the drop-down menu.
- Click the Windows
Start button and select Control Panel. 
- Under Programs, click Uninstall a program if you are using the default category view,
...or click Programs and Features if you are using the large/small icons view. 
- Right-click your version of Avast Antivirus, then select Change from the drop-down menu.
- If prompted by the User Account Control dialog for permissions, click Yes.
- When the Avast Setup wizard appears, the following options are available:
- Optionally change the default location where your modified version of Avast Antivirus will be installed.
- Use the drop-down menu to select components according to Custom protection, Recommended protection, or Minimal protection. If you choose Custom protection, manually select or de-select components.
- Click Change to confirm.
- Avast Premium Security 19.x
- Avast Free Antivirus 19.x
- Avast Omni 1.x
- Avast Internet Security 19.x
- Avast Pro Antivirus 18.x
- Microsoft Windows 10 Home / Pro / Enterprise / Education - 32 / 64-bit
- Microsoft Windows 8.1 / Pro / Enterprise - 32 / 64-bit
- Microsoft Windows 8 / Pro / Enterprise - 32 / 64-bit
- Microsoft Windows 7 Home Basic / Home Premium / Professional / Enterprise / Ultimate - Service Pack 1, 32 / 64-bit