To replace a paper file, you must first log in as a Director or Track Director.
For papers that have not been completed and added to the list of completed submissions go to your Submissions queue, and click on the In Review link. You'll be presented with a list of presentations in review. Click on the title name of the presentation you wish to edit, and upload a galley file under Layout.
For papers that have already been completed, you can go to your Submissions queue, and click on the Presentations link, where you will be presented with a list of already-completed (ie., published) presentations. Click on the title name of the presentation you wish to edit. You'll see that under Layout you can edit or delete an already-uploaded file; you can also upload a new, or additional files as well.