Problem with margins

Question

I need to set margins. The odd pages should have left margin 3.5 cm and right margin 2.5 cm. The even pages should have left margin 2.5 cm and right margin 3.5 cm. I tried to do it but for example by option \oddsidemargin the left margin on odd page moves to the right but the right margin shrinks.

The .cls file is HERE.

Document:

\documentclass[thesis=B,czech]{FITthesis}[2012/06/26]

\usepackage[utf8]{inputenc}

\usepackage{graphicx}

\department{text}
\title{text}
\authorGN{text}
\authorFN{text}
\authorWithDegrees{text}
\supervisor{text}
\acknowledgements{text}
\abstractCS{text}
\abstractEN{text}
\placeForDeclarationOfAuthenticity{text}
\declarationOfAuthenticityOption{1}
\keywordsCS{text}
\keywordsEN{text}

\begin{document}

\begin{introduction}
    %
\end{introduction}

\chapter First


\begin{conclusion}
    %
\end{conclusion}

\appendix

\end{document}

Answer 1

I answer myself.

To add...

\usepackage[inner=3.5cm,outer=2.5cm]{geometry}

...is solution.