macOS version 10.14 or later

How do I download the version of macOS version of 10.14? I cant download Microsoft Excel and it also is not letting me update my microsoft word app and is telling me to do the macOS version 10.14 but when i go to the app store to update it says that i do not have anything else to update. This has never happened to me before i don't know if its a bug or if there is something wrong with mac