Make your changes, and then click the Save Job button.
Your changes will appear on your Careers Page immediately. The job boards will update your job with your changes within 24-48 hours.
If you want to edit multiple jobs at once, you can edit the job template from which a job was posted (if you have multiple jobs posted from a template). After you save the job template, select the option to apply your changes to existing jobs posted from this template. Edit job templates by navigating to Account > Manage Job Settings > Job Templates and clicking the 'Edit' link next to the job template you wish to edit. More info: How do I add job templates?
Note: Editing a job posting will not refresh the job. You must refresh the job by clicking the refresh button. More info: How do I refresh my job postings?