The refrigerator's owner may be able to solve a lot of the problems causing poor cooling, but if not, an appliance repair professional can complete the job. Trying the do-it-yourself options can save the expense of a service call.
The first place to look is at the temperature control dial. Other people in the home may have adjusted it the wrong way. Then check the vents inside the refrigerator and freezer units. If too much food is in the way, air can't get from the vents to the rest of the unit. Pulling the refrigerator out to look at the coils, either on the back or underneath, to see if dust is in the way, may solve the problem. Cleaning dust and debris off the coils can improve cooling performance.