The Refrigerator Has Stopped Cooling Properly

Over the past couple of days, I've noticed that the food in the refrigerator isn't staying cold enough, even though the appliance itself is still running and the light inside turns on. At first, I thought the settings might have changed by accident, but the temperature is still higher than usual. Can you tell me what people usually check in this situation, and when it's time to call for refrigerator repair?