\documentclass{beamer}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[polish]{babel}
\usepackage{newtx}
\usetheme{Warsaw}


\begin{document}

\begin{frame}
\frametitle{Symulacja działania WF-sieci}

\begin{center}
\only<+>{\includegraphics{wfnet1.pdf}}%
\only<+>{\includegraphics{wfnet2.pdf}}%
\only<+>{\includegraphics{wfnet3.pdf}}%
\only<+>{\includegraphics{wfnet4.pdf}}%
\end{center}
\end{frame}

\end{document}