How do I adjust the brakes if the braking force is too weak or too strong?

If the braking force is too weak, loosen the braking arm nut with a wrench, slightly lengthen the brake wire to make its tail longer, then tighten the nut and test the brake. If the braking force is too tight, follow the same process but adjust the wire to make the tail shorter. Always test the brake after making adjustments to confirm the braking force.