Due to weather and temperature changes, your house, doors, and windows are going to expand and contract during heating and cooling cycles. The benefit of sliding doors is that they allow for the expansion and contraction of adjustable rollers, allowing you to tilt the door within the frame, raise or lower the door, based on your needs.
Unlock and open your patio door a few inches. For Marvin windows, you will be inside for one of the adjustments, and outside for the other on either end of the door. Pella and Andersen allow you to adjust your sliding glass doors from the inside.
Remove the plugs above your door's rollers on the interior of your home. If the interior of your door is wood, you may need to score the perimeter of the plugs, and use a flat head screwdriver to turn out the plugs.
Examine the distance between the top of the door and the frame and the bottom of the door and the frame called the reveal. You should be able to eyeball them to see if they are even all the way across. If not, you will know which side of your sliding glass door to raise or lower.
Turn the screwdriver in the hole where the plug was, depending on the side that needs to be raised or lowered, or both sides if the whole door panel needs to be raised or lowered. Your goal is to get the reveal to be even all along the door on the bottom and top of the door. Turn your screwdriver left or counterclockwise to lower the door and right or clockwise to raise the door.
Slide your glass door back and forth a few times to check for ease of operation. If it is gliding smoothly, you have resolved the problem. If not, keep playing with the adjustments to get the door square within the frame.
Replace the roller's plugs, and close and lock the door. Make sure you aren't feeling any air leakage around the operating panel. If you are not, and the door slides well again, you are finished.