Here I've used a 13mm open end spanner to remove the gear selector cables from its pivot.
The vehicle in the video is an Astra K, though I've used this method on almost every car I've had to remove them on. The spanner face will need to be narrow enough to fit between the ball joint & selector linkage. The linkage will come off easily if levered directly vertical, but will resist if at an angle
Video from Vehicular Maintenance