You should be able to access the newest version if you purchased before. Chapter 5 is a new download with all the content up until now packed in it.
There are some issues if you carry over your old save. I would recommend a fresh in this instance.
Further, I am not sure if the old save will be compatible even. But if you want to try, you can put the saves in the new save folder which should be in the appdata folder if you're on windows. You can find it by hitting windows key + R, then type %appdata% . The filepath is AppData\Roaming\RenPy the folder is stronggirls