To view all of your jobs that need to be refreshed, click on the Needs Refresh section on your Jobs tab, or view your ToDos in the Account Activity section of your Dashboard.
Postings can only be refreshed every 30 days. If there is a Refresh button underneath your job posting, your job is no longer very high up on the job feeds and should be refreshed if you are still hiring. If there is no refresh button, your job posting is not yet ready to be refreshed. Your job can be refreshed 30 days after it was first posted or most recently refreshed.