Take the roller assembly to a home-improvement store. I would caution against buying the rollers first because there are about 40 different styles and buying the wrong one is common.

To keep the sliding glass door from sticking, you need to replace the rollers on the bottom of the door. This is not hard, just a little cumbersome. The door is large and somewhat fragile.

High-nice sliding door tracks and rollers are crucial for clean operation. They save you traumatic door jams, squeaks, and difficult beginning/last motions, providing a trouble-loose experience.