Choose the "Lexer Language" for which you would like to make the change (e.g. Python):
Click "All Fonts"
Choose the font and size you would like to assign.
AFAIK there's no global mechanism to configure fonts for all lexers as once (there's a default, but it's only for unrecognized languages).
In:
Settings| Preferences| Highlighters| Styles
Choose the "Lexer Language" for which you would like to make the change (e.g. Python):
Click "All Fonts"
Choose the font and size you would like to assign.
AFAIK there's no global mechanism to configure fonts for all lexers as once (there's a default, but it's only for unrecognized languages).
HTH