How do I get letter sized paper when I am using the res.cls margin option

Question

Here is the first part of my code sorry I'm new to TeX but this is really annoying me also using the geometry package doesn't work and neither does

\documentclass[margin, letterpaper]{res}
...
...
% LaTeX resume using res.cls
\documentclass[margin]{res}
%\usepackage{helvetica} % uses helvetica postscript font (download helvetica.sty)
%\usepackage{newcent}   % uses new century schoolbook postscript font 

\setlength{\textwidth}{5.2in} % set width of text portion
\usepackage{enumitem}
\addtolength{\textwidth}{.5in}
\addtolength{\textheight}{2in}
\addtolength{\leftmargin}{-.1in}
\begin{document}

% Center the name over the entire width of resume:
 \moveleft.5\hoffset\centerline{\large\bf Stephen Leone}

% address begins here
% Again, the address lines must be centered over entire width of resume:
\raggedright \hspace*{-\sectionwidth}{287 Warren Avenue}\hfill sml94@live.com\\
\raggedright \hspace*{-\sectionwidth} {Hawthorne, NY 10532}\hfill (914) 980-4235\\
\vspace{4mm}
% Draw a horizontal line the whole width of resume:
\moveleft\hoffset\vbox{\hrule width 505 pt height 1pt}\smallskip

\begin{resume}


\section{EDUCATION} {\sl Bachelor of Engineering} in Electrical Engineering, Expected Spring 2016\\ 

Answer 1

This is what I would do to get your above code working. I am not sure what you were intending to achieve with the dimensions / margins, edit as necessary.

\documentclass{article}
\usepackage[letterpaper,top=3cm,bottom=3cm,left=2cm,right=2cm]{geometry}

\usepackage{helvet} % uses helvetica postscript font (download helvetica.sty)
\renewcommand{\familydefault}{\sfdefault}

\usepackage[parfill]{parskip}

\usepackage{titling}
\author{Stephen Leone}
\title{Resume}

\begin{document}
    \pagestyle{empty}
    \begin{center} \large\textbf{\theauthor} \end{center}

    \begin{minipage}{0.2\textwidth}287 Warren Avenue\\sml94@live.com\end{minipage}%
    \hspace{0.6\textwidth}
    \begin{minipage}{0.2\textwidth}Hawthorne, NY 10532\\(914) 980-4235\end{minipage}%
    \smallskip
    \hrule

\section*{EDUCATION} \textit{Bachelor of Engineering} in Electrical Engineering, Expected Spring 2016

\end{document}

Answer 2

I tried to go as minimal as possible. Gives me letter as default...check the settings on your front end:

\documentclass[margin]{res}

\begin{document}

% Establish mywidth as width of entire resume (since res.cls co-opts textwidth!):
\newlength\mywidth
\setlength\mywidth\textwidth
\addtolength\mywidth{\sectionwidth}

% Center the name over the entire width of resume:
\moveleft0.5\hoffset\centerline{\Large Stephen Leone}

% Contact info centered over entire width of resume:
\raggedright \hspace*{-\sectionwidth}{287 Warren Avenue}\hfill sml94@live.com\\
\raggedright \hspace*{-\sectionwidth}{Hawthorne, NY 10532}\hfill (914) 980-4235

% Draw a horizontal line the whole width of resume:
\moveleft\hoffset\vbox{\hrule width \mywidth}

% Begin the resume environment:
\begin{resume}
\section{EDUCATION} {\sl Bachelor of Engineering} in Electrical Engineering, Expected Spring 2016.
\section{HOBBIES} {\sl Engineering} I do engineering in my free time as well!
\section{LOVES, LUSTS, \& ALLEGIANCES}  Just engineering.  Engineering, engineering, engineering.

\end{resume}
\end{document}