I have a magic chef model# CSD2123AR and is isn't holding the right temp. any ideas? I have heard of people changing the thermostat that might be bad.

Bad thermostat control is certainly a possibility. But, what have you done so far? Are you allowing sufficient time after adjusting the temperature setting, for the temperature to stabilize. Mine requires 24 hours between adjustments.

Before you do anything clean the coils under the unit along with the fan. Dirty coils are the number one cause of it not holding the temperature. It cannot cool with dirty coils and will keep shutting off on overload until the compressor burns up. Wash the coils out with spray soap and a hose nozzle then vacuum up water with wet-vac. It will work much better clean. Allow to run for 24 hours and see how it is doing then.

Agreed, clean the coils under the fridge. Also, check the seals on the door. Make sure the fridge/freezer is closing, and the seals are tight. Sometimes clean the seal with water.

Also, is it not generating cold? Or not keeping cold?