You can put smaller wheels and tires on the Ranger Sport. But the change in diameter will reduce the circumference of the tire which will have your speedometer showing you are driving somewhat faster and will make your odometer show that you have covered more distance than you have. It may also decrease your actual fuel mileage a bit while showing you have covered more miles per gallon since the engine and transmission will actually have to turn faster to make the same speed on the smaller diameter wheel-tire combination. You may also notice a difference in ride quality, but that could be a plus or a minus, right?
The original Size: P255/70R16 tires are about 30" in diameter. The 2wd model of the 2010 Ranger Sport was sold with 15" wheels using Size: LT235/75R15 tires which are about 29" in diameter. I don't know if Ford compensated for the difference in overall diameter when they set up the speedometer and odometer and the sensor or cable drive that runs them. A good tire store will know about this difference and advise you accordingly. BUT you probably need to ask them about it specifically.
If you get wheels that are the same diameter and width as what came on the 2WD Ranger Sport I would expect it to work OK with the differences I noted above. If you are doing this for Looks alone, and care not about the price of the change or the cost down stream of tires or fuel used over the long haul I don't imagine any real problems other than the Speedometer/odometer question.