Office 365 is installed as a 32-bit program on your Windows PC by default.
Microsoft recommends the 32-bit version, even on 64-bit systems, to avoid compatibility issues with third-party add-ons. However, there may be instances when you’d want the 64-bit version, like if you’re using a very large database or worksheet.
If you need the 64-bit version of Office, follow these steps:
STEP 1. Go to Office.com and log in using your Microsoft account
STEP 2. Click on the Install tab
STEP 3. Click on the Language , 32/64-bit, and install options link
STEP 4. Select the Version drop-down box and select Office 64bit. Then click on Install to download the small install file for just one computer or click on Download offline installer for the large installer if installing on multiple computers.
STEP 5. Once you have downloaded the 64-bit install file, run the downloaded file to setup and complete the installation
Remember that you can’t have both the 32-bit and 64-bit versions of Office installed at the same time. If you already have the 32-bit version installed, you’ll need to uninstall it before installing the 64-bit version. For more details on the differences between the two versions, refer to Microsoft’s documentation.