how do I change the coolant?

I would definetely reccomend a shop for working with jaguar cooling systems, extremely complex and there are alot of items that can break on these cars if your not careful. Alot of the hoses under the hood are hard plastic and get brittle and crack as well as the coolant resoiviors crack on these alot.

IT is always quite hard Just steady pressure counter-clockwise, maybe with a rag or rubber mat will do it.