Park the car on level ground. Remove the key of your Jaguar X-type from the ignition.
Open the trunk and locate the battery. If the dead battery is preventing you from opening the trunk automatically, open it manually: fit your key into a small hole on the lower side of the trunk deck lid and turn it.
Locate the positive and negative terminals on the top of the battery. You will recognize the positive and the negative terminal by the '+' and '-' signs, respectively. Do not touch the positive and negative terminals at the same time and never let the terminals touch each other.
Remove the cable from the negative terminal first, using your hands or a flat head screwdriver. Remove the cable from the positive terminal.
Detach the battery from its housing. The housing depends on the Jaguar x-type model. Loosen the battery and remove it completely from the car. Be very careful when carrying a car battery--they are heavy, and you can hurt and/or burn yourself it you accidentally drop it.
Clean the tray where the battery sat, as well as the cables that you detached from the battery with a clean cloth. Use a mild cleaning solution made of lukewarm water and a teaspoon of baking soda to wipe the cables and clean the tray. Wait for the tray and the cables to dry completely.
Place the new battery inside and secure it in place. Secure the new battery in the same position and manner as the old battery. Make sure that the terminals are in the same position as the old battery.
Reconnect the cables, starting with the positive one, then the negative. Be very careful to connect the terminals to the right cable.
Recycle your old Jaguar car battery by returning it to the store or taking it into a local recycling center. Never dispose of the old battery with the ordinary trash.
Start the car to check that everything is working properly.