The wind turbine has a tower; a nacelle; and a hub comprising a hub connection flange for being detachably connected to a blade connection flange of a rotor blade. The method comprises the next steps: fixing a first positioning element in the nacelle or in the top of the tower; fixing a second positioning element to the blade in a root blade area; lifting the blade to the vicinity of the hub connection flange by means of lifting means; putting into contact the first and the second positioning elements; providing an accurate position of the blade connection flange, prior to the connection to the hub connection flange, by cooperation of the first and second positioning elements; and providing, when the first and the second positioning elements cooperate, a trajectory of the blade which is parallel to the axis of a hub connection hole, disposed in the hub connection flange, the provision of the trajectory being carried out by means of a guided element joined to either the first positioning element, the second positioning element, or both.