That's done in the shift box mounted on the motor. The cable runs through the transom shield and up to the shift box. There are large slotted screws on the cover plate, remove them. Once that's done you will see the big black cable has two small cabled with round stops no them that lift out of the shift quadrant. push on the black cable to relieve the tension on the cables and remove the ends from the quadrant.
There's a keeper mounted on the outside of the transom shield, with one screw that holds the cable in place. Carefully remove that screw and keeper. Lots of penetrating oil helps. Where the cable goes through the shield there's a rubber stopper molded into the black cable. Work it free and the cable will pull out.