freezer and fridge are not cold enough?

I have a roper RT21LMXKO05 refrigerator and the freezer won't get colder than about 10 degrees.the fan is blowing into the freezer and the fridge part.It runs all the time but almost every day when I get home from work it is not running and the freezer is about 40 degrees,if I turn the thermostat up and down 2 or 3 times it starts running again a few minutes later but still no colder than 10 degrees.The fridge is only a couple years old.