How can I change the font size of the title and the font size of the authors in Latex?

This will let you put whatever font you desire in the title: (just replace \myfont)

\documentclass[11pt, a4paper, twocolumn]{article}
\begin{document}
\font\myfont=cmr12 at 40pt
\title{{\myfont Who knows}}
\author{{\Huge A.~U.~Thor}}
\maketitle
Paper.
\end{document}

You can also use \Large or \Huge instead of \myfont, to fit the rest of the document style (this way LaTeX will only change the size of the font)