This is because an upgrade process will still leave several (support) components installed.If you only want to install Outlook 2016 and combine it with Office applications of previous versions of Office see the Outlook 2016 compatibility with previous versions of Office section later in this guide.If any such application is still installed, you will not be able to install the 64-bit edition of Office.
If the update isn’t being offered to you yet, go to: File-There is no need to uninstall your current Office 365 installation first.
When it comes to Outlook, there is no direct benefit of having the 64-bit edition instead of the 32-bit edition.
For more information see: Should I install the 32-bit or 64-bit version of Office/Outlook?
Note: In order to use some of the functionality in Outlook 2016, you’ll need to configure your Exchange account with Cached Exchange Mode enabled (CEM). For an overview of features requiring CEM see: Outlook 2010: New features and Cached Exchange Mode Microsoft still recommends installing the 32-bit edition of Office 2016 instead of the 64-bit edition unless you have a specific need that requires the 64-bit edition of Office 2016.
However, when you have a 64-bit edition of Windows and you know that all your add-ins and other applications that rely on Office support the 64-bit edition of Office 2016, you can safely install the 64-bit edition.
This is because your previous settings are being migrated.