If the smell is coming from outside the refrigerator, you could have a dead rodent in the compressor or drip pan area. To check this area, unplug the refrigerator and pull the rear bottom service panel off of the outside of the unit. This should give to access to the compressor and defrost drip pan. Check this area carefully. Check the defrost drip pan for any foreign matter that could be smelling bad.
If the smell is coming from inside the refrigerator and/or freezer compartments, follow these odor removal tips:
To remove strong odors, place some shallow trays of the following items on the shelves inside your refrigerator:
Activated charcoal (can be obtained from pet supply store, usually used in aquarium filters)
Fresh, unused coffee grounds (this will leave a coffee smell that will eventually dissipate over time)
Once most of the strong odor is removed, you may need to keep a small bowl of the deodorizer in the back of one of your refrigerator shelves
Also, throw out your ice in your storage bucket below the automatic ice maker once the strong odor is removed -- ice cubes will absorb and retain the refrigerator odor
Constantly keeping an open box of baking soda in the refrigerator will minimize odors
Keep foods that are stored in the refrigerator and freezer properly wrapped and sealed to that they are air tight to prevent food odors from building up in these compartments
If the odor is so strong that the above methods do not help, you may need to take more aggressive steps to remove the odor. This would involve removing all of the food in the refrigerator and freezer. Prepare more trays of a deodorizing agent listed above. Turn the refrigerator off and place the trays in the refrigerator for a couple of days or until the odor is gone.
If you need more help, resubmit your question with additional details.