When you delete a presentation, it will automatically appear in the Trash bin. To locate and view your deleted presentations, go to your library and click on Trash at the bottom left corner of the Library Sidebar.
To recover deleted presentations, click on Trash and then click on the drop-down arrow at the bottom right corner of your presentation. Select Recover From Trash and the presentation will automatically appear in your library.
Your presentations will remain in the trash can until you empty it. Once you empty your trash can, there is no way to get your presentations back.