Add Logo to LaTeX poster

One way is to add this after your \begin{document}:

\addtobeamertemplate{headline}{} 
{
\begin{tikzpicture}[remember picture,overlay] 
\node [shift={(-10 cm,-5cm)}] at (current page.north east) {\includegraphics[height=5cm]{logo}}; 
\end{tikzpicture} 
}

I had to compile twice.

You can use the tikz package to accomplish this easily. Working with the template you mentioned, you have to include:

\usepackage{tikz}

in the preamble. Then, in the body of your document (right after \begin{document}) add the following:

\addtobeamertemplate{headline}{} 
{\begin{tikzpicture}[remember picture, overlay]
     \node [anchor=north east, inner sep=3cm]  at (current page.north east)
     {\includegraphics[height=5cm]{logo}};
  \end{tikzpicture}}

which yields the following output (zoomed-in to the top right corner):

You then can of course adjust the dimensions of the logo by specifying different values in the square brackets right after the \includegraphics command.

Lastly, inner sep specifies de diagonal distance to the top right corner.

Hope it helps!