You can not edit your submission which has been accepted (green), refused (red), or reviewed (white). If you want to make changes to these submissions, you must contact the conference administrator. The contact link is in the conference menu.
However, if your submission is in the “Initial” stage (no action by reviewers or coordinators), you can go to the My space menu and click on the small pencil to the right of your submission to make changes.
Similarly, if the status is Awaiting for Update, just click on the pencil to edit your deposit.