Don't I get Microsoft Excel for free?

To the best of my knowledge Microsoft does not give their Office suite away on Windows or Macs. You can use the online version free however: https://products.office.com/en-us/free-office-online-for-the-web

Another alternative that is free and quite good is Libre Office: https://www.libreoffice.org/

Most likely you have an older 32 bit version of Office. As I understand it Office 2016 or later can be upgraded to 64 bit operation, but not the older versions. So, it is either buy or subscribe to a newer version, or start using one of the other programs mentioned.