Upgrade/Downgrade depends on certain factors:
1) Tire size calculation, cannot be more ore less than 3% of OE size
2) Size of brake caliper, some car has a big caliper and cannot install smaller wheel
The best is to call your dealer, to ask what is the smallest rim the car will fit.
Then use the above chart to determine the tire for your car.
You can get a 285/30R22, but it will be very expensive and some sizes don't even have snow tire.
The above tire size is based on mathematic formula and won't exceed the 3% threshold and so its alright.