Glass sliding doors (generally known in Arizona as patio doors) run on any variety of rollers and tracks. If the door is no longer gliding easily, the bearings in the rollers have deteriorated. If it is a nylon roller, the nylon roller is simply either cracked, chipped, or worn down to the point that the door is dragging on the track.
Open the door half way and, with the help of another person, lift the door and sling the bottom of the door to the inside of the house. You should then be able to drop the head of the door out of the track and have the operating leaf of the patio door in your hands. Set it on edge and remove the rolling assembly at the bottom of the door. Most hardware stores carry universal rollers that will fit into most arcadia door configurations.