Il y la commande `\setbeamerfont{alerted text}{size=\Large, series=\bfseries}` text}{attributs}` voir page 196 et 197 de la doc
à utiliser comme suit, par exemple
\setbeamerfont{alerted text}{size=\Large}
\setbeamerfont{alerted text}{series=\bfseries}
\setbeamerfont{alerted text}{shape=\itshape}
\setbeamerfont{alerted text}{family=\rmfamily}
\setbeamerfont{alerted text}{size=\Large, series=\bfseries, family=\rmfamily}
**Remarque** une variante étoilée existe `\setbeamerfont*`
**Exemple**
\documentclass[11pt]{beamer}
\usetheme{Warsaw}
\setbeamerfont{alerted text}{size=\Large, series=\bfseries}
\begin{document}
\begin{frame}
\frametitle{What Are Prime Numbers?}
\begin{definition}
A \alert{prime number} is a number that has exactly two divisors.
\end{definition}
\begin{example}
\begin{itemize}
\item 2 is prime (two divisors: 1 and 2).
\item 3 is prime (two divisors: 1 and 3).
\item 4 is not prime (\alert{three} divisors: 1, 2, and 4).
\end{itemize}
\end{example}
\end{frame}
\end{document}
