Topping up the clutch fluid in an Iveco?

Can anyone tell me where to top up the clutch fluid in an Iveco please? I've tried googling but can't find anything. It's a horsebox that hasn't done much work over the winter and gears are a little bit stiff. They ease off when the clutch is pumped a few times and it has been suggested it just needs clutch fluid. Would like to try that before giving myself a mechanic's bill (horsebox mechanic is not local so travelling just to look is £50). Thank you.