You would have to buy new rims to put a 16" tire on. this is how the tire "numbers" work.
195 is the width of the tire tread in millimeters.
65 is the "aspect ratio." that means the distance between the rim and the top of the tire.
15 is the rim size
To go to a 16" would require a different rim, and that would get expensive.
to check what is available in your tire size, go to this website
http://www.tirerack.com
you don't have to buy from them, but that will tell you what brands are available in that size.
Sams Club or Walmart is a good place to buy tires, and at good prices. Be sure to shop around because tire prices, even the same tire, vary a lot from shop to shop