My Maytag refrigerator is not cooling both in the upper and lower compartments. The model is M1TXEMMWB00 and it is approximately 3 years old. What is the problem and how do I fix same?

On the coldness range dials do you have them in the middle
Like 3 for 1-5 or C for A-E
If you have them too low they will not get cold enough
If you have them too high the freon will freeze

I don't know anything about checking the freon level
But whenever I scrap fridges that people tell me quit working there is usually hardly any freon in them

You may need a new fridge.

More than likely your coils are dirty under the unit and need to be washed out with spray soap and water using a water hose nozzle. You will have to unplug the fan motor and remove it to be able to get to the coils and clean them well. Do not try taking a shortcut on this and not flush out the coils well or it will burn up the compressor. Also, make sure to clean the fan blades. You will have to remove the back after unplugging it, first. Remove and wash out the drain pan, too. You should also remove the front kickplate and clean it, too. If the rear cover has a vent in it, make sure to clean it, too. Here are some manuals: https://dl.dropboxusercontent.com/u/8010163/Maytag%20Refrigerators.zip

One more note: Don't worry about "Freon" levels. If you need refrigerant you have a leak and refrigerators do not leak under normal circumstances unless you have been around the coils with an ice pick or knife trying to defrost it. If we were talking about a car where you have a leak problem built in due to a shaft and pulley with a seal then it could leak, but modern refrigerators are sealed and there is no way for them to leak and if they do it's a major problem requiring about $300 worth of work at minimum to find the leak, weld it up, install a drier, vacuum it down, and then charge it with about 12 oz. of R-134a. Refrigerants do not wear out. It lasts forever. There are refrigerators over 50 years old still running fine and no gas has ever been added.