There are a number of reason the fridge may no longer be cooling.
In order to identify the root cause, I would first check the what value the thermostat is set to which is found at the top right of the fridge, it should be set at a medium value of around 3 or 4.
Next check the radiator at the back of the fridge, it should be warm\hot to touch, this is a good sign as it shows the compressor is working.
The next thing to do is check the door seal, to see if there are any tears or cracks in the seal, as this may result in the fridge losing its coolant.
Lastly I would turn the fridge off for 1 hour, give it a good clean inside ensuring all moisture has been removed, then turn it back on with the thermostat to medium (3), keep the door closed for 2 hours, and then check the temperature.
Please let me know what you discover after performing these checks, and I can advise how best to proceed.