How to get Office 2016 if you have a one-time purchase of Office 2013 or an older version of Office
If you installed a one-time purchase of Office 2013, you can't upgrade directly from within the Office 2013 software. You'll need to either purchase one of the Office 2016 suites of products, such as Office Home & Student 2016, or purchase an Office 365 subscription.
For more information about the different options available for purchasing Office 2016, see Choose your Office.
See Also
Can I upgrade to Office 2016 for Mac from Office for Mac 2011?
How do I get the newest features in Office 2016 for Office 365?