Sliding doors have a screw located on the side of the door on the bottom and also on the end that butts up to the wall that has the latches.
Most of the time, the wheel is in OK condition, it just fills up with dirt, grime, and junk. The screw one way makes the wheel come down more and the other directon makes the wheel recess more.
Usually, the door will work fine by making the wheel come down more and then cleaning the track and then liberally spraying with WD-40.
If this is not the case, all doors and put in with about an inch of space between the door and the top of the frame. This is why the door goes in by setting the top in the frame and raising up allowing room for the bottom to go on the track and once on the track you gently let it down with all its weight.
To take the door off, you just raise up within the frame, the door will go up a good inch or so, then when fully up, pull the bottom off the track and walla, the door is off.
Insert back just the opposite manner.
Very easy. Watch for heavy wind or lack of sufficent balance as the door will get away from you then you will get a new set of wheels with a new door.