A traditional remedy for this is to put an open box of Arm & Hammer baking soda in the fridge. But if you have a serious odor problem I suggest you empty the fridge. Defrost it. If there's a water catch tray underneath, emopty that out. Wash the interiors of the fridge with a good disinfectant. Then put a couple boxes of baking soda in there.
You can find more info here
https://www.google.com/search?hl=en&output=search&sclient=psy-ab&q=keep+refrigerator+from+smelling&btnG=