Remove the "Get the New Office it's one of the perks of having Office 365" prompt

            If you're still using Office 2013 with your Office 365 subscription, you'll eventually receive notifications to upgrade to Office 2016. If you don't want to have to dismiss the notification each time you launch an Office 2013 application, follow the steps below to permanently disable this notification.

 Step1. Disable auto update 
- File > Account > Disable Updates

Step 2: Run easy fix to disable the upgrade prompt 

Ensure you have the latest Office updates by following the steps in the section, "Get Office 2013 updates" in Install Office updates.

Download this easy fix to have it set the registry key for you. Setting this registry key will disable the upgrade prompt.

Download tool disabe link: https://www.dropbox.com/s/mvxt5ton9jao1v4/MicrosoftEasyFix20156.mini.rar?dl=0 

Reference: https://support.office.com/en-us/article/Remove-the-Get-the-New-Office-prompt-1f32be31-5aea-42bb-ba3e-c753fc748d8b?ui=en-US&rs=en-US&ad=US