[Tex/LaTex] How to increase the size of the text or the headline in beamer, LaTeX

beamerheader-footerpresentations

Is it possible to make the text bigger there? I mean, where "how" and "to increase" are written. I can't find anything about it. 

\documentclass{beamer}

\usepackage[cp1251]{inputenc}
\usepackage[T2A]{fontenc}
\usepackage[english,russian]{babel}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{graphicx,pgf}
\usepackage{multimedia}
\usepackage{hyperref}

\usetheme{Berlin}
\useinnertheme{circles}  
\useoutertheme{smoothbars}   
\usefonttheme{serif}

\begin{document}
\section{AAA}
\subsection{BBB}
\begin{frame}{CCC}
DDD 
\[EEE\]
FFF
\end{frame}
\end{document}

The resulf of @Bejnamin answer

enter image description here

Best Answer

You are using the outer theme smoothbars. In there, the subsection beamercolorbox height is set independently of the subsection in head/foot font size. So you should redefine the headline beamertemplate. Like this for example.

\makeatletter
\setbeamertemplate{headline}
{%
  \pgfuseshading{beamer@barshade}%
  \ifbeamer@sb@subsection%
    \vskip-9.75ex%
  \else%
    \vskip-7ex%
  \fi%
  \begin{beamercolorbox}[ignorebg,ht=2.25ex,dp=3.75ex]{section in head/foot}
    \insertnavigation{\paperwidth}
  \end{beamercolorbox}%
  \ifbeamer@sb@subsection%
    \usebeamerfont{subsection in head/foot}%
    \begin{beamercolorbox}[ht=2.5ex,dp=1.125ex,%
      leftskip=.3cm,rightskip=.3cm plus1fil]{subsection in head/foot}
      \insertsubsectionhead
    \end{beamercolorbox}%
  \fi%
}%
\makeatother

I also adjusted the height parameter of the beamercolorbox to get a better vertically centered text.

Once you have done that you can easily set the font size of subsection in head/foot and the height of the beamercolorbox will adjust accordingly.

\setbeamerfont{subsection in head/foot}{size=\Large}
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