If you want to know how to renew avast free license, you can follow the step given below:
1. Restart Windows in Safe mode and run this utility.
2. Use the Browse button to find and point it out.
3. Click Uninstall.
4. Then the program asks for confirmation to delete the folder, click Yes.
5. After successful removal, the program asks for a reboot, agree.
6. You can here delete the folder AVAST Software in Program Files.
Hopefully above steps will help you to fix the issue if not you can also follow our blog to see more on cannot open avast user interface.