The rollers could be bad and that is hard to tell until you have tried everything and then finally pull the door out to check them.
Your track could be worn. You can replace this or cover it with a stainless steel track cover.
If it is an adjustment problem, your door should have a tendency to rock while you roll it. To check the adjustment, close the door until there is just a crack of light showing through between the door and the jamb. This crack should be even from top to bottom. Further info on adjustment is available here
. We also may have most of the parts you need.