Right here is my guide on how to do it after battling with it myself. It is a relatively easy job although fiddly and painful at times 
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Tools & Parts required:-
.Tools & Parts required:-
- Socket set:- Namely 6,7,10,12,13mm Sockets
- Various Spanners
- Trolley Jack:- To raise car up of the ground a bit to save your back
- A relatively long flat blade screw driver.
- Misc Jubilee Clips (If they still have original Fiat clips)
- 7 Litres ready mixed coolant
Part 1 - Drain Coolant & Achieve Access
To begin with you will need to drain your coolant, I didn't bother with this as I put a tray under the car to collect it once I remove the thermostat. To do this simply remove a coolant hose towards the bottom of the coolant system.
The Thermostat is located to the right hand side of the engine bay underneath the Air Inlet tubing.
To begin with Jack the car up to a height you feel comfortable working at. You then need to remove the battery. This is easily done by removing the 13mm Hex nut on the bracket on the left hand side of the battery and undoing the battery terminals. Make sure you have your Red key to hand just in-case although wasn't required for me
Next it's time to remove the Air Inlet host which is bolted to the engine with 2 x 10mm Hex Bolts, As well as the crankcase breather hose and the coolant hose. Your engine bay should now look something like this revealing the all important thermostat:-
There are 4 coolant hoses running to the thermostat as well as a coolant temperature sensor (Blue).
Thermostat Removal & Refitting
Remove the hoses one by one, be careful with the temp sensor as its a flat spring clip and it's very easy to loose it after removal.
Once removed you can undo the 2 10mm bolts that bolt the thermostat to the engine block and remove the thermostat.
It maybe worth while cleaning the contact area with alcohol and a rag to remove contaminants likely to disturb the seal on the new thermostat.
You will need to remove the coolant temperature sensor and refit to the new thermostat. I did this by using a long socket.
Refitting is simply the same process in reverse. My advice would be to connect the back hardest to access hose one the far left first then connect the thermostat due to access:-
Notice the bleed screw. The other one is located on the radiator itself.
When refitting things should start looking like this:-
Good luck and have fun and as always Safety First
