SIEMENS TALL FRIDGE iQ700 KS36FPI30

I don't know what is wrong but the bottom part of the fridge is working perfect but the upper part isn't cold.
The fridge is 5years old so it's a bargain if someone knows how to fix it :)
I can deliver. (collection NN2 8PZ)
Thank you

Design features

Stainless steel anti-fingerprint door with silver painted sides
Net capacity: 300 litres
Electronic controls
LED display
5 safety glass shelves
FlexShelf
Vitafresh section:
2 x 0°C ‘dry’ drawers on telescopic rails
1 x 0°C ‘moist’ drawer on telescopic rails

Dairy compartment
LED interior lighting
SuperCool function with automatic deactivation
Active cooling with interior fan
Acoustical door open warning signal
Removable magnetic door seals
Left hinged reversible door
Height adjustable front feet
Noise level 41 db
Energy rating A++
Annual energy consumption 124 kWh
Dimensions: H186 x W60 x D65cm
To achieve the declared energy consumption, the attached distance holders have to be used. As a result, the appliance depth increases by about 3.5 cm.