A method of replacing a generator of a wind power installation. The generator is provided in the interior of a pylon of a wind power installation and the pylon has a door opening. An exchanging cross beam is fixed by way of a first fastening point to a crane hook of a mobile crane. A first end of the cross beam is introduced with a second fastening point through the door opening into the pylon. The transformer to be replaced is fixed to the second fastening point of the first end. A compensating weight is fixed at the second fastening point to the second end of the cross beam. The second end of the cross beam is tilted or inclined until the transformer is at the height of the door opening and the crane hook is moved until the transformer to be replaced is outside the door opening.