Disassembly is pretty simple. Removing the back (and top if necessary) will reveal the insulation, possibly 2 layers. It is fiber glass so wear gloves, long sleeves and eye protection. If the line from the temp probe is not visible, you will need to remove the first layer of insulation carefully and set it aside. You will see the temp probe going through the insulation and smoker wall. It may be captured by a threaded nut. Loosen and remove, then remove the probe. The LINE is a very thing hollow tube with liquid in it. This is what operates the switch. As the fluid expands it closes the switch via a diaphragm and the power to the element comes on. As it it cools it flows away from the switch which opens breaking contact.
Installing a new unit is the reverse. BE CAREFUL! The line/tube, while sturdy, cannot get kinked or it will block the flow. It will come coiled up. Drop the probe through the hole below where the controller mounts and secure the new controller and carefully pull the probe down and secure. Put the insulation back in place and you are finished. The kit will come with instructions.
Good luck.