How do you put your convertible top down with key remote on a 1999 jaguar xk8?

I don't know if the remote will do it, but if you stick your key into the door it will put it up and down depending upon which way you twist the key.

That's correct. You cannot open or close the top with the fob, but you can do it with the key in the door. By the way, most people use their door keys so infrequently that the mechanism is usually very stiff at first. You might have to jiggle is back and forth several times to exercise it before it finally starts to work. Don't turn the key too hard, though. The connection between the latch and the lock pushrods is plastic and it can be broken.