Is the freezer OK but the fresh food section is not.
If that is the problem then check that the damper is operating correctly.
First check/clean the condenser coils.
Clean the condenser fan blades. Also check that it is running properly.
Check/clean the vents at the front and back of the unit.
Check that the evaporator fan is running correctly.
Remove the cover in the freezer and check the evaporator coils.
If they are heavily iced over then it is probably a defrost problem.
If there is frost in just one area usually where the freon enters the evaporator then it is probably a sealed system problem.