Select the office product you want to download and install on the device.
Go to the office.com/setup option. To upgrade Office, press on the products of office.com/setup and start downloading and installing Office products on the device.
log in and enter office 25 digit product key to activate your office product.
if you are new user then you need to create a office account to get more benefits of office.com/setup subscription.

https://sites.google.com/view/wwwsofficecomsetup/
https://sites.google.com/view/wwswofficecomsetup/
https://sites.google.com/view/urlsitewww/office-setup