Installed Catilina, how do I update Word?

If you have an early version of Office for Mac 2016, you can update it at no charge. See: https://docs.microsoft.com/en-us/office365/troubleshoot/administration/office-2016-for-mac-64-bit-upgrade

If you have Office for Mac 2011 or earlier, you can either subscribe to Office 365 or you can make a one-time purchase. See: https://products.office.com/en-us/buy/compare-microsoft-office-products-for-mac?ms.officeurl=mac-compare-redir

Or the free Microsoft Office on the web: https://products.office.com/en-us/frhttps://www.libreoffice.org/

Or Google Docs: https://www.google.com/docs/about/

Other options include using the free and very good Libre Office https://www.libreoffice.org/

or Apple's Pages and Numbers

You'll probably need to access you Microsoft account. Having done so you'll see:

From here, choose search and search on update office. You should see this link https://support.office.com/en-us/article/Install-Office-updates-2ab296f3-7f03-43a2-8e50-46de917611c5. It looks like the link should eventually get you where you need to go. There are other links that also could be helpful after searching on update office.