New

After selecting New from the File menu a dialog will appear asking if you wish to save changes in the current slide show.  Selecting yes will Save the current slide show with all changes made since it was opened under its current file name. 

User Note: A Save operation cannot be Undone. It is always good practice to rename a slideshow before continuing work on it to recover from any errors you may have inadvertently made.
The New function may be selected from the File menu, by entering the shortcut key command ctrl+N or by clicking on the New icon

Selecting New will clear all slides from the Views and provide a new starting point for the creation of a slide show.