Changing the bullet style in Beamer

The following minimal working example shows how one can change bullet style of different itemize levels using \setbeamertemplate command:

% Bullet style in Beamer
\documentclass{beamer}

% Theme choice
\usetheme{CambridgeUS}


% set the itemize item symbol as a diamond
\setbeamertemplate{itemizeitem}{\scriptsize$\diamond$}

% set the itemize subitem symbol as a triangle
\setbeamertemplate{itemize subitem}{\scriptsize$\blacktriangleright$}

% set the itemize subsubitem symbol as a circle with a dot
\setbeamertemplate{itemize subsubitem}{\scriptsize$\odot$}


\begin{document}

\begin{frame}
\frametitle{Bullet style in Beamer}
    \begin{itemize}
        \item Level 1
        \begin{itemize}
            \item Level 2
            \begin{itemize}
                \item Level 3
            \end{itemize}
        \end{itemize}
    \end{itemize}
\end{frame}


\end{document}

Compiling this code yields:

We used diamond shape for main items, right triangle for subitems and a circle with a dot for subsubitems.

For more details, I invite you to check Lists in Beamer – Complete Guide.