Two reasons that i can think of that would require you to adjust the height of the door.
Adjusting bifold doors height.
To adjust a door in this instance i either use better longer wood screws and try to fix deeper through the frame into the timber stud behind that the frame is fixed to.
Adjusting bifold door height is accomplished by using the second adjustment feature of the bottom pivot pin.
As a last resort loosen the top pivot bracket setscrew and slide the top away from the door frame.
Squirt some pva wood glue in to the screw holes first then bang in as many match sticks as will fit.
Bifold doors contain two separate door panels that are connected with hinges forming one bifold door.
Adjust these as needed to maintain the height.
Open the bifold doors slightly and the hardware is where the doors hinge.
Adjusting the height of the inner edge of the bifold doors doesn t require you to remove them from the brackets so the process is a fairly simple one.
Some doors will have nuts attached to the bolts so that the height can be locked in place.
To replace the door follow the steps in photo 2 in reverse order.
Turn the bottom pivot height adjustment to lower it if possible.
Here your main concern is with the hinge bolts.
Not sure if this is your problem.
Locate the bolt positioned at the bottom and extend it in order to lower the bifold door or retract it to make the door higher.
If your bifold doors are dragging however and appear to be sitting a little low or are sometimes popping out of their track when you use the door you can adjust the height using the hinge bolts until they stay in place extending it to raise the doors and pushing it in to lower them.
Alternatively plug the screw holes with a rawl plug or lots of matchsticks.
Whether your bifold doors contain two panels or four panels adjust the doors similarly if they continually pop back open after you close them.
If you extend these bolts the door will be raised.
Or gently lift the door off the lower bracket with a flat pry bar.