This question appears regularly on this particular site section. Firstly, is the freezer side cold? If so, it's likely a problem with the diffuser. This is a small door like device controlled by the fridge thermostat that opens and closes as required and is located between the freezer and the fridge. Most folks don't know that the compressor/cooling device only produces cold air that goes into the freezer side, at least in the majority of fridge/freezer combos here in the U.S. The diffuser then lets sufficient cold air into the fridge side. The opening/ closing, as I said, is controlled by the thermostat, which could also be suspect.
Secondarily, see if there's any kind of ice build up in the freezer side, which would indicate a possible failure of the automatic defrost function with which most models is equipped. This is correctable by most moderately useful DIY'ers, but I'll not describe the process unless you need it...
Best of luck!