I've read about changing the shape of the itemize bullet in the
Beamer class documentation and also on this question which shows how to change the bullet shape to a checkmark (
Where can I find the complete list of the bullet shapes available for the Beamer class?
You'll find those predefined templates in the documentation. Here are those which are listed in the guide (Chap. 12 Structuring a Presentation: The Local Structure p. 111)
Furthermore you can define your very own items: