Cold air enters the fridge through a damper or vent between the freezer and fridge. The evaporator fan in or behind the freezer blows the air through. There is an adjustment to open and close this vent to allow more or less cold air in. Make sure the fan is running and that the air is being blown into the fridge.
If the evaporator coils behind the back panel of the freezer are icing up because of auto defrost failure that will stop the circulation of cold air and eventually affect the freezer too.
check defrost timer, defrost heater, defrost thermostat
In most of the new units they now have the evaporative defrost control. It senses when to defrost based on how many times and for how long the door is opened. It's more energy efficient but there does seem to be lots of problems with the board.
Post your model number for more information. | 
Refrigerator side not cooling enough, freezer is fine. 
