Just losen it enough to move around. It is threaded into a plate that moves around so you can adjust it. I took some gasket material and made a round gasket for the washers so they wouldn't scratch the paint in the doorjams while I was adjusting it.
Are you sure that the sriker needs adjusting and you don't have some worn out hinge pins/bushings? Grab the door when its open and see if it wiggles up and down. There is no point in adjusting the striker if it is your hinges that are shot.