[Tex/LaTex] Make text bigger in beamer

Question

How can I make my text in the beamer presentation bigger? The size of frametitles and so on are okay, but the normal text in the slide is relatively too small.

\documentclass[compress,black]{beamer}

\usetheme{Szeged}
\useoutertheme[subsection=false]{smoothbars}
\usefonttheme{serif}
% - I need a darkred background color in the sections bar (at the top) on all slides.
\setbeamercolor{section in head/foot}{bg=red!50!black}

% - Just beneath the sections bar I need a narrow darkblue bar on all slides.
\makeatletter
\AtBeginDocument{
    \usebeamerfont*{headline}
    \colorlet{global.bg}{bg}
    \usebeamercolor{subsection in head/foot}
    \usebeamercolor{section in head/foot}
    \usebeamercolor{frametitle}
    \pgfdeclareverticalshading{beamer@barshade}{\the\paperwidth}{%
       color(0ex)=(blue);%
       color(1ex)=(blue);%
       color(2ex)=(section in head/foot.bg);%
       color(7ex)=(section in head/foot.bg)%
    }
    \pgfdeclareverticalshading{beamer@aboveframetitle}{\the\paperwidth}{%
       color(0ex)=(blue);%
     color(1ex)=(blue);%
       color(2.5ex)=(section in head/foot.bg)
     }
    \pgfdeclareverticalshading{beamer@belowframetitle}{\the\paperwidth}{%
      color(0ex)=(global.bg);%
      color(1ex)=(frametitle.bg)
    }
}
\makeatother

% - Nothing should be displayed on the bottom bar of the slides (no authorname, no section, etc)
\setbeamertemplate{footline}{}

% - All text should be in black.
\setbeamercolor{title}{fg=black}
\setbeamercolor{frametitle}{fg=black, bg=white}

\title{Long Title}
\author{Author}

\begin{document}

\begin{frame}
    \titlepage
\end{frame}

\section{One}
\subsection{One}
\begin{frame}
    \frametitle{ABC}

    This text is too small!
\end{frame}

\end{document}

Answer 1

From the beamer user guide, section "18.2.1 Choosing a Font Size for Normal Text"

• \documentclass[12pt]{beamer}Makes all fonts a little bigger, which makes the text more readable. The downside is that less fits onto each frame.

• \documentclass[bigger]{beamer} Same as the 12pt option.

• \documentclass[14pt]{beamer} Makes all fonts somewhat bigger. Requires extsize to be installed.

• \documentclass[17pt]{beamer} This is about the default size of PowerPoint and OpenOffice.org Impress. Requires extsize to be installed.

• \documentclass[20pt]{beamer} This is really huge. Requires extsize to be installed.

---

Edit after a MWE was added:

The above procedure seems to conflict with \AtBeginDocument{\usebeamerfont*{headline}}, but you can do

\makeatletter
\AtBeginDocument{%
    \usebeamerfont{headline}%
    \colorlet{global.bg}{bg}%
    \pgfdeclareverticalshading{beamer@barshade}{\the\paperwidth}{%
       color(0ex)=(blue);%
       color(1ex)=(blue);%
       color(2ex)=(section in head/foot.bg);%
       color(7ex)=(section in head/foot.bg)%
    }
    \pgfdeclareverticalshading{beamer@aboveframetitle}{\the\paperwidth}{%
       color(0ex)=(blue);%
       color(1ex)=(blue);%
       color(2.5ex)=(section in head/foot.bg)%
     }
    \pgfdeclareverticalshading{beamer@belowframetitle}{\the\paperwidth}{%
      color(0ex)=(global.bg);%
      color(1ex)=(frametitle.bg)%
    }
    \fontsize{20}{24}\selectfont%
}
\makeatother