A hoisting system includes an upper cable support system to be mounted on a top end of a wind turbine, a lower cable support system at a lower end of the wind turbine, and left and right cables extended between the cable support systems. A clamping yoke arranged approximately at the centre of gravity of a rotor blade includes left and right climbing systems adapted to climb on the cables with first and second rollers spaced in a longitudinal direction of the blade whereby the first rollers are nearer a root end of the blade than the second rollers. A position at least in the longitudinal direction of the blade of the first roller of at least one of the left and the right climbing systems is adjustable by an actuator.