Replacing garage door rollers is the likely option when they are beyond lubrication. The rollers can seize up, making them unusable. Or they can get so noisy that it is torture to raise the door.
Do you have a different problem? See 'Overhead Garage Door Repair' for a complete listing of the garage door topics.
The rollers are available at most home supply stores and are fairly inexpensive. Take one of the old ones with you when you go shopping.
The roller rides in the track, but you do not want to take the track off to replace a roller. It is easier to take the hinge off that has the sleeve for the roller. With the hinge out of the way the roller comes out easily.
Use a wrench to take the bolts out of the hinge. Only take one hinge off at a time. Removing too many hinges will compromise the support for the door. You can also use a battery drill and a nut driver to remove the bolts from the hinge.
Slide the new roller into the sleeve in the hinge. Install the hinge and you are done. Use the same method to replace the bolts that you did to remove them. The bolts are just lagged into the metal or wood on the door, so, don't over tighten the bolts. Now that was easy. Like I said, not much to dealing with the door rollers.