I do not have any more details for you, but in general, I would think that the easiest way to do it would be to bring the entire unit down from the ceiling. So, unplug it, disconnect the opener from the door, unbolt the opener from the ceiling and lower it to the floor, remove the pin or bolt holding the track to the door header, and lower that end to the floor. Before going another farther, I would measure exactly where the trolley is on the track, in order to minimize adjustments later. Then I would slacken the belt or chain, get it out of the way, and unbolt the opener from the track. Then, I belive that you will have a stop bolt in the track, which you can remove, after which the trolley should slide off the motor end of the track. Reassembly would simply be the reverse, but before connecting the belt or chain, make sure that the trolley is back to the point where it was when you started. I would be concerned though as to the reason that the trolley failed. It could be something as simple as faulty metal or design, but with the opener removed, check the door; you should be able to raise and lower it with relative ease, and the springs should hold it in the open position. If you determine that the springs are not balanced properly, or if you have any doubts, contact a competant door company in your area. Also check the tracks and rollers, to ensure that it is operating smoothly. Be careful; a garage door is generally the heaviest moving object in a home.