Get a free diagnosis before you call a repair pro or buy parts.
Common causes include dusty condenser coils (the fridge can't shed heat), a failed evaporator fan, worn door seals letting warm air in, a defrost problem icing over the airflow, or blocked air vents inside. Which one it is changes the fix from a five-minute cleaning to a real repair — that's what a diagnosis narrows down.
Keep the doors closed as much as possible. Perishable food held above 40°F (4°C) for more than about 2 hours should be discarded — when in doubt, throw it out. A closed fridge holds safe temperatures for roughly 4 hours; a full freezer for about 48 hours.
It depends on the cause. Dirty coils, a fan, or a seal are inexpensive relative to replacement. A sealed-system problem on an older fridge often isn't. A diagnosis first tells you which side of that line you're on before you pay for a service call.