How do I update microsoft office and excel to 64-bit I am using OS Mojave 10.14.4

If you have a 32 bit version of Office for Mac 2016, you can update it. See: https://support.microsoft.com/en-us/help/3187505/office-2016-for-mac-64-bit-upgrade

If you have a version older than Office for Mac 2016, you will need to replace it by either buying a new standalone version or subscribing to Office 365 when a version of Mac OS is released that will not support 32 bit apps. Or continue to use a version of Mac OS that does support 32 bit apps.

Also see: https://products.office.com/en-us/buy/compare-microsoft-office-products-for-mac

Microsoft will do it if they haven't already done so years ago. This isn't something you can do other than make sure that when Apple eventually requires it the software you buy will work. Everybody has a lot of lead time on this and many changed to 64 bit years ago. You only really need worry if you have some beloved application from 2002.

32-bit app compatibility with macOS High Sierra 10.13.4 and later

https://support.apple.com/HT208436

How to Find All 32-Bit Apps on a Mac

http://osxdaily.com/2018/03/06/find-32-bit-apps-mac/

ASC post summarizing this:

https://discussions.apple.com/thread/250076499?answerId=250135608022#250135608022

Only Microsoft Office 2016 is up-gradable to 64 bit.

Office 2008, and 2011 are 32 bit, no longer supported and cannot be updated. Office 2018 is already 64 bit from the get go, so no need to update it.

For Office 2016 the regular software updates should have taken care of that in 2018: https://support.microsoft.com/en-us/help/3187505/office-2016-for-mac-64-bit-upgrade