Using the columns environment in beamer one can easily align two images side by side in frame, so that both images take up the whole side they are assigned.

The following minimal working example shows how to do this:

% How to align two images side by side in beamer
\documentclass{beamer}

% Theme choice
\usetheme{CambridgeUS}

\begin{document}

\begin{frame}{Side by side images in Beamer}{Bottom vertical alignment}

% start the columns environment and set the
% positioning of the content inside the columns at
% the top with the T specifier

\begin{columns}[c]

% create the column with the first image, that occupies
% half of the slide
\begin{column}{.5\textwidth}
\begin{figure}
\centering
\includegraphics[width=0.8\textwidth]{Block-Diagram.png}
\caption{Block diagram of a 1st order system.}
\end{figure}
\end{column}

% create the column with the second image, that also
% occupies half of the slide
\begin{column}{.5\textwidth}
\begin{figure}
\centering
\includegraphics[width=0.9\textwidth]{Step-Response.png}
\caption{Step response of a 1st order system.}
\end{figure}
\end{column}

\end{columns}

\end{frame}

\end{document}

Compiling this code yields: