Run Avast and then follow the screens below.
You can click on an image to make it larger.

1

Click Maintenance

2

Click Register Now

3

Click Select for Standard Protection

4

You only need to enter your personal eMail address. You can ignore the rest of the fields. Then click the green Register button.

5

Click the link UNDER the green button or close the box. You do not want to try any additional protection. (It can hang here for a while)

 

You should now see on the registration page that you are registered for 365 days.  You will receive an eMail asking you to confirm your address.  You should click the link in the eMail.  It will ask you to create a password.  I do not bother with that.  I just close the browser and get on with my life.