\documentclass{beamer}
\usepackage[orientation=landscape,size=a1]{beamerposter}
\usetheme{uclposter}
\useinnertheme{blockborder}
\setbeamercolor{block body}{bg=white,fg=black}
\title{Title of the Poster}
\author{Author 1 and Author 2}
\institute{%
Department of Statistical Science,
University College London
}
% \beamertemplategridbackground[1cm]
\setbeamersize{text margin left=2cm,text margin right=2cm}
\newlength\blockcolsep%
\setlength\blockcolsep{2ex}
\newlength\postercolumnsep%
\setlength\postercolumnsep{2cm}
\newlength\postercolumnwidth%
\setlength\postercolumnwidth{0.3333\textwidth-0.66666\postercolumnsep}
\newlength\totalwidth%
\setlength\totalwidth{\textwidth+3ex}
\begin{document}
\begin{frame}[t]{}
\centering
\begin{columns}[totalwidth=\totalwidth]
\begin{column}[t]{\postercolumnwidth}
\centering
\begin{block}{Step 1}
Some content
\end{block}
%
\begin{block}{Step 2}
\begin{itemize}
\item Item 1
\item Item 2
\end{itemize}
\end{block}
%
\begin{block}{Step 3}
Sample
\end{block}
\end{column}
%
\begin{column}[t]{\postercolumnwidth}
\centering
\begin{block}{Step 1}
Some content
\end{block}
%
\begin{block}{Step 2}
\begin{itemize}
\item Item 1
\item Item 2
\end{itemize}
\end{block}
%
\begin{block}{Step 3}
Sample
\end{block}
\end{column}
%
\begin{column}[t]{\postercolumnwidth}
\centering
\begin{block}{Step 1}
Some content
\end{block}
\begin{block}{Step 2}
\begin{itemize}
\item Item 1
\item Item 2
\end{itemize}
\end{block}
\begin{block}{Step 3}
Sample
\end{block}
\end{column}
\end{columns}
\end{frame}
\end{document}
