how do I upgrade microsoft office to be compatible with catalina OS?

Depends on the version of MS office you have. 2011 and earlier cannot be updated. 2016 can be updated, and 2019 and 365 are already 64 bit so do not need updating.

If you have Office 2011 or earlier it cannot be updated, and you would need to purchase a new version directly from Microsoft or subscribe to the 365 option in the Mac app Store.

Office 2016 for Mac 64 bit Upgrade - Microsoft.com

Buy new Microsoft Office Products - Microsoft.com

Purchase new office:

https://products.office.com/en-us/compare-all-microsoft-office-products