Hold the center shaft of the strut with a 3/8" wrench while removing the nut at the top of the strut with an 18mm wrench.

Slide the nut over the cable and remove it

When reassembling, torque the nut to around 35ft-lbs.

If you don't have an open-ended 18mm socket, get a good feel for the torque when you remove the nut so you can reassemble similarly.