[Tex/LaTex] Change the font size in the book class

document-configurationfontsizetemplates

I'm using thesis template of my University with pre-defined page properties. I need just to change the font size from 11 to 12.

You can edit it directly through the sharelatex.com

Link to my project: open please Chapter 3: Proposed algorithm.

Many thanks for any advice.

enter image description here

P.S.:

0) It's a new project with new properties, the old my question I removed.

1) I've tried geometry package, but still changing font changing margins as well

2) I can't remove "twoside" from the documentclass, due to the fact that in the future I will print that thesis.

P.P.S. with David's code it looks better, but margins are still not the same.
enter image description here

Best Answer

There are just four relevant lengths for the horizontal setting.

At 11pt 

\documentclass[11pt,a4paper]{book}


\typeout{tw: \the\textwidth}
\typeout{os: \the\oddsidemargin}
\typeout{es: \the\evensidemargin}
\typeout{mw: \the\marginparwidth}

\begin{document}

zzz

\end{document}

produces

tw: 360.0pt
os: 22.0pt
es: 70.0pt
mw: 106.0pt

If you change to 12pt you get

tw: 390.0pt
os: 10.0pt
es: 52.0pt
mw: 88.0pt

but you want the 11pt widths so set them back:

\documentclass[12pt,a4paper]{book}

\setlength{\textwidth}{360pt}
\setlength{\oddsidemargin}{22pt}
\setlength{\evensidemargin}{70pt}
\setlength{\marginparwidth}{106pt}

\typeout{tw: \the\textwidth}
\typeout{os: \the\oddsidemargin}
\typeout{es: \the\evensidemargin}
\typeout{mw: \the\marginparwidth}

\begin{document}

zzz

\end{document}
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