I have open source Qt 5.8 and simply want to upgrade to version 5.15. I go to Qt website and see "download the online Qt installer" and on another Qt site I see "offline Qt installer."

1. Which one do I download?
2. Will my version of Qt Creator (currently it is 4.2.1 based on Qt5) also be updated when I download a new version of Qt or is that a separate download?
thanks