The rear derailleur is pulled further towards the small sprockets by the built-in spring. If you turn it outward (away from you), you increase the tension on the Bowden cable and pull the rear derailleur towards the larger sprockets. Proceed in small steps according to the grid of the screw. A quarter turn is often enough. When should you increase the tension and when should you decrease it? It's easy to tell:
- If the chain won't shift to the next smaller sprocket: reduce tension
- If the chain jumps down one sprocket too far: increase the tension
- If the chain won't shift to the next larger sprocket: increase the tension
- If the chain jumps too far up the cassette: reduce the tension
Until all gears shift up and down smoothly, it may be necessary to shift the cassette several times in both directions, making small corrections every now and then. With a new Bowden cable, it can happen that the cable stretches a bit, and the cable housing becomes wedged in the guides. This may make subsequent corrections necessary. With a little practice, you'll be able to do it even when you're on the go.