How do I update my computer from the 32 bit Microsoft Office?

See my post here. It can all be done through the Apple online store.

Best to remove Office 2008/2011 from your Mac before upgrading to Catalina or Big Sur, by using the uninstaller in the Microsoft applications folder. Your MS documents are unaffected by the 32/64 bit application issue and should be safe on a Time Machine backup.

By purchasing a newer version.

There's the subscription Office 365 (now called Microsoft 365). For $100 per year, you can install it on up to any six devices you own.

Or, the one-time cost, perpetual license Office 2019. $150 for student/home version (Word, Excel, PowerPoint), and $250 for the business version that includes Outlook.

You can get either 2019 title for less than Microsoft's direct cost. $219 for the business version and $125 for the home/student version at Amazon.

You purchase Office 2019 from Microsoft or subscribe to Microsoft 365.

Look into the Free LibreOffice, it handles MS Office files like Word & Excel…

https://www.libreoffice.org/