How do i change page sizes in the document ?

[Martina Schwarz van Doorn]

Dear LyXers,

can anyone tell me how change page sizes in a document ? In the main
part of my thesis, i want to use a wide margin because it is more
legible, but in the appendices, where i want to include my code in two
columns, i want to have small margins in order to save space. 

I tried something like:


\setlength{\textwidth}{140mm}
\setlength{\headwidth}{\textwidth}
\textheight=214mm
\oddsidemargin=8mm
\evensidemargin=8mm
\topmargin=2mm
\renewcommand{\baselinestretch}{1.3}

in the preamble (which seams to work allright), and then after \appendix
tried 

\setlength{\textwidth}{180mm}
\setlength{\headwidth}{\textwidth}
\textheight=214mm
\oddsidemargin=0mm
\evensidemargin=0mm
\topmargin=2mm
\renewcommand{\baselinestretch}{1}
\begin{multicols}{2}
\verbatiminput{main.f}
\end{multicols}

in TeX-mode, but this only messes up my headers and keeps the code as
messed up as without it.

Thanks 

Martina