I read the answers here and they were abundantly unclear. So here is a better answer, complete with screenshots. I am aware that there are shorter ways to do this, but they are error prone. This is the simplest way I know to do this.
On the taskbar, you can view your notifications pane by clicking this button on your taskbar:
The notifications button is white when you have new notifications. As you can see, mine is black because I've cleared all my notifications. When you click it, it brings up this pane, usually on the right side of the screen for me.
Here you can see things like your wifi and bluetooth. Click on the "All Settings" button there to access the settings screen:
Notifications are under system settings, so click the "System" button.
Here you can manage lots of things about your computer, but we only care about notifications. So click "Notifications & Actions" to get to the notifications tab
Here you can control what notifications you want to see. Find "Get Office" under "Show Notifications from these apps" and turn it "Off".