Text Formatting ⇒ Beamer navigation bar

[Jack26]

Hi,

With beamer, I am trying to have a special header (navigation bar) on each of my page but there is something I can't do.

For example, with the Berlin theme. On each page, I have a navigation bar with the sections and another navigation bar, below, with the subsections for the given section. Both the sections and subsections fonts are small.

First, I would like to see only the sections on the header and
secondly, I would like them to be a lot bigger.

Any suggestion ?
I tried some things with "\setbeamertemplate{headline}" but without succes.


Thank you very much for your help.

Jack