I had Free version 4.8. Today I get the pop up notice saying it will expire soon. With no directions/instructions found on how to keep my free one, I downloaded the new free version 5. Everything installed ok but, I see it will expire this Sept! How can this be? The old free version I had for over a year. Has something changed about the free version?
Its ok you just have to re-register come sept.
That is a trial version, you have to go in the maintenance tab from the main user interface, and click register. Don’t worry, registration is free, and in version 5, the process is much less of a hassle. 
If you installed avast 5.0 free over 4.8 Home, it should have retained your registration details as part of the installation process (which first uninstalls 4.8.).
If you did a clean install of 5.0 then you would only have 30 days trial before needing to register, so that doesn’t fall in line with the expiry in September.
No matter though two weeks before expiry you will start to get registration notifications and the avastUI Summary section will allow for re-registration through the avastUI for another year.