Not sure what the ball looks like in your door but in the ones I've had, you can just lift the door out of the track by lifting it into the upper track and letting the bottom come out of the bottom track. Set it on the floor and tip it back. Be careful as these doors may be pretty heavy. If you can lay it on horses, you'll be able to see the ball mechanism and you may be able to remove it from the door and lubricate it. If not, you can just use one of the spray lubricators like WD-40 or spray on silicon. Work the ball around once you've sprayed it and you should be fine. Just put the door back the way it came out.

Good Luck.