You want to edit your vehicle to change the fuel type. Go to your land rover page and look for the [EDIT CAR] link under the title. Click that. At the top of the next page the first line is, "Current Type:" followed by model information. Click "[change type]" at the end of that line.
When you do that you'll see a form on the page that's similar to the form you used when you created the car. Look for the "Engine:" menu at the bottom. Change that to the correct engine. If you don't see a diesel engine option, choose 'Other' from the list for more options.
Then, whatever body style I choose, engine type is greyed out and not selectable.
Ahh, managed to work around it. I selected the wrong year deliberately and suddenly engine type came available! I chose diesel and then corrected the year back. So I am sorted, but there is a problem there.
Anyway, thanks for the help and keep up the good work with the site.