Kegorators are rarely automatic defrost, so you need to unplug them and let them defrost about every 2-3 months. Even if you don't see it, if the internal parts of the compressor lines get gunked up with frost, the kegorator won't get very cold.
Take everything out, unplug the kegorator, and leave it overnight to defrost (maybe put a towel or pan in it, there will be about a gallon of water that drips out). Plug it back in once it's all defrosted, and it'll get back down to the lower temps, and remember that you need to do this about every 2-3 months or so.
That's usually the problem when kegorators aren't getting super cold. Most kegorator thermostats are set from about 40F-60F.
If you actually need to adjust the thermostat, find where the thermostat is located (usually on the back in one of the upper corners behind a panel) and it'll have a screw on the actual mechanical thermostat. Turn that screw counterclockwise, and it changes the range of the mechanical thermostat. Just be careful, you don't want frozen beer!
