Open your Pella sliding door halfway. Find the small plastic cap on each edge of the sliding door panel near the bottom.
Pry the caps away with a putty knife to access the roller adjustment screw for each roller. Turn the screw clockwise with a Phillips head screwdriver to lift the door panel off of the lower track if the door is rubbing against the lower track. Turn the screw counterclockwise to lower the panel if the door is rubbing against the top track.
Adjust the roller on the opposite side in the same manner. Open and close your Pella door to test the panel's operation. Continue making adjustments as necessary. Push the caps back into the adjustment holes once you finish.