Glassdoor is a jobs and career marketplace that is changing how people search for jobs and how companies recruit top talent. The very upper portion of the track on the inside was removed down to floor level; when the door is installed it still fits below this level and is thus still supported but would now clear the lower track when raised into the upper track. Although typically held in place with a single screw your door will likely be slightly different and you will have to find the screw(s) that hold the assembly. There are many more, but make absolutely sure you are purchasing the correct assembly for your door.
Fit the new assembly (or the old one with new rollers) into the door frame in the same manner they came out and put the fastening screws back into the frame. It is wise to adjust the rollers up into the door as far as possible to make installing the door easier; the next section gives those instructions. The door is re-installed the same way it came out: insert the door into the upper track and slide the bottom of the door over the lower track. The center of the door should line up on the section of track the roller rides on, but it can be moved later if you find during the roller adjustment phase that it isn’t centered properly.
The top screw is to remove the assembly, while the lower on is the adjustment screw and is reached through a hole in the door frame. Using a screwdiver (probably a phillips type), turn the adjustment screw until the door itself is raised just slightly off the bottom track. As the adjustment screw is turned it pushes the actual roller wheel down which is what pushes the door up. Your door is ready for many more years of service and it didn’t cost an arm and a leg to do it.
This screw will probably be turned in a clockwise motion to move the roller down and the door up, but it may be necessary to turn it the other way depending on the assembly that fits your door. Expect the screw to turn quite easily for a few turns but then get considerably harder to turn as the roller comes into contact with the track and begins to raise the door.
It may help to raise the door very slightly with a screwdriver or prybar as that will make it easier to turn the adjustment screw. Just don’t raise it so far that the roller comes off the track and allows the bottom of the door to move sideways. Adjusting this screw is done to accomplish two things; to raise the door so that it does not drag on the bottom and to plumb the door.