Many wooden sliding glass doors have tandem roller assemblies that allow it to slide smoothly open and closed.
(*Note: If you have a metal sliding door, see How to Adjust the Rollers on an Aluminum Sliding Glass Door.)
These rollers are vertically adjustable, so the wheels can be raised or lowered to raise or lower your door panel within its frame. The higher the door is raised, the tighter it fits. In order to remove the door panel from the frame to make repairs or whatnot, it is a good idea to lower the panel to make it easier to remove.
The rollers typically adjust from the inside. There may be a small plastic plug at the bottom of the door panel. Remove this--it should easily pop out with the help of a flat pry bar or screwdriver. Removing the plug exposes the adjustment screw on the roller.
Depending on which particular rollers you have, you need to use a flat-head or phillips screwdriver to adjust the rollers.
Some roller assemblies turn clockwise to raise the panel and counter-clockwise to lower it (like the roller shown below); other brands are the opposite. Carefully try turning your screwdriver one way or the other to figure out which direction you need to turn.
Our advice: if you're adjusting the rollers to fit the panel square in the frame, adjust BOTH rollers so that the panel is sitting as low as it can go and both rollers are adjusted to the lowest position. Then, adjust both rollers the same amount, little by little, until the door panel is in the desired position. For example, make one full turn of the screwdriver on the first roller, then do a full turn on the other roller. Repeat.
If you adjust the rollers differently, the door won't sit square and flush in the frame, and your sliding door will not slide smoothly, and you could jamb the lock.
All About Doors & Windows carries a huge inventory of sliding door rollers, including the one shown above, which replaces rollers in Peachtree, Andersen, Caradco, Jeld-Wen, Hurd, and Pozzi doors, among others: part #13093.
**We have also written an article specifically for replacing Andersen rollers: How to Replace Andersen Rollers