Upgrading to Mac OS 10.15

I’m sorry if this has been asked before - I have a MacBook Air running OS 10.14. Want to download OS 10.15. According to my system report most applications will work on OS 10.15 64-bit except for Word for Mac 2011. So I intend downloading LibreOffice. My question is which do I download first - Mac OS 10.15 or LibreOffice?