Sometimes floor sre so far out of level it is very difficult to get a door to close flat. That said, it is fairly easy to adjust the spings so the closes as flat as possible. Extension springs(run along the track sides) are fairly easy to adjust. Rasie the door and prop it up, loosen or tighten the cable on the spring as needed, lighter on one side VS the other. Torsion springs(coiled springs on a bar over the top of the door), are much more difficult, and dangerous for the average DIY.