Open Excel and click Check for Updates on the Excel Help menu.
If you are not subscribed to Microsoft 365 that may update your Excel some but it will not update it to the current version.
Microsoft does not provide free upgrades between major versions of their Office products (unless you subscribe to Microsoft 365).
If you have a version of Microsoft Office that is not compatible, you can either subscribe to Microsoft 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 use the free and very good Libre Office https://www.libreoffice.org/
or the free Microsoft Office on the web: https://products.office.com/en-us/free-office-online-for-the-web
or Google Docs: https://www.google.com/docs/about/
or Apple’s Pages and Numbers