Unfortunately you are a little late. A year ago you could have had a free upgrade to 2016.
Now, there is no discounted "upgrade" path. MS marketing figures they have us addicted to Office so they no longer have to offer price incentives to user to upgrade. You just pay the full price for the new license you want.
PS: If you find a link to a MS Store page for onetime payment Visio 2016, let us know. I've been looking and all I've found is the 2 subscription offers at the MS Store and a bunch of internet stores offering standalone visio at absurdly low prices, ie $25-60.