How to increase font size in vlc

Dear all,
I have bought the original (read it: original) Simpsons season 1 and Family Guy season 1.
These dvds have subtitles for different languages like EN,FR,DE.Whatever subtitle I select I can not increase its size. I have the same problem in these two different tv series.

In vlc I go to settings->subtitles and I select as font size Larger… \

Unfortunately there is no change.
Do you know what might be the problem?

Best Regards