The problem is most likely not in the thermostat,
Several things you need to do first :

Reset you control knobs to factory reccomended settings (middle of knobs).

Check and reset air control knob on left side wall, beside crisper drawer(1/2 to 1/3 open).

The lower crisper on this unit is for "meat" not vegetables or fruit.
(you need to switch articles).

Check and make sure there is nothing on the shelves that would direct the air down the back or side walls forcing the air down to the bottom of compartment.

After 24 hours, check the temperature(s), freezer should be 0 dgrs and fresh food should be 38 dgrs(+/- 2 dgrs,factory reccomended temps).

If adjustment is needed, move knob 1 setting at a time(approximately 3 dgrs per setting) in desired direction(colder/warmer).

Please try these reccomendations, before replacing any parts, I think you'll be happy with the results.