Since this class is based on the book class, one can take a look at that. Then you will realize that \chapter uses \@makechapterhead which is responsible for this spacing. You can change the original code (from book.cls) accordingly in the preamble:
\makeatletter
\def\@makechapterhead#1{%
\vspace*{0\p@}% This is generating the additional space. default {50\p@}
{\parindent \z@ \raggedright \normalfont
\ifnum \c@secnumdepth >\m@ne
\if@mainmatter
\huge\bfseries \@chapapp\space \thechapter
\par\nobreak
\vskip 20\p@
\fi
\fi
\interlinepenalty\@M
\Huge \bfseries #1\par\nobreak
\vskip 40\p@
}}
\makeatother
A word of caution: This is a well established standard. I wouldn't suggest to do big changes to that. But in the end it's up to you—your gusto and decision.