How do you change the image of a bullet point in LaTeX Beamer

You can simply set a symbol of your choice. Let me assume you’d like the \checkmark symbol, just write:

\begin{itemize} 
    \item[\checkmark] one
    \item[\checkmark] two
    \item[\checkmark] three
\end{itemize}

Furthermore, if it’s too long to write, you can set a new command:

\newcommand{\myitem}{\item[\checkmark]}

and the whole thing becomes:

\begin{itemize} 
   \myitem one
   \myitem two
   \myitem three
\end{itemize}

Otherwise, you can use the enumitem package as stated in the answer below.

For document classes other than beamer, there are two more ways to do the trick:

In the preamble, write:

\def\labelitemi{\checkmark}

If you want to change the symbol in only one itemize environment, write:

\begin{itemize} 
\newcommand{\labelitemi}{\checkmark}
   \item one
   \item two
   \item three
\end{itemize}