If you wish to close or turn off a job posting, navigate to Jobs from the left menu, and select the job in question.

On the menu on the upper right, under Job Actions, select Close Job.

A modal window will appear where you can select the reason for closing the job.

Select the Close Job button.

If you wish at any point to reopen a job, filter for closed jobs on the jobs page, select the job, and choose Reactivate This Job from the Job Actions section of the page: