The alphabetical List will show you all of the Posters at a glance, and will allow a moderator to edit, delete, and set permissions for each poster.
To edit a poster, open the site's admin and open Posters>List.
Click the title of the poster that you want to edit to enter it's Detail/Update page.
To delete, tick the box next to each poster that is to be removed, and click the Delete button to remove them from the site.
You can change permissions settings for each poster by, again, ticking the box next to the poster, and then clicking the Permissions button.