impress; font change

Readers,

Please, how to perform a font change to a presentation? The function 'select all' only seems to work for selection of a text frame, or a presentation slide, not the entire document of all presentation slides.

To do that you should look at the Styles you have and change the font
there. And where the Styles are depends on whether you are using the
built-in slide text boxes (Presentation Styles), or adding Text boxes
(Drawing Object Styles). If you use Styles consistently it is easy to
change the Font definition.

Regards,

Change the font in the slide master, and then reapply the slide master
to all slides (of course, this means that the slide master has been used
in the right way).

The usual key f5 doesn't work in impress, so how to show the 'styles' dialogue windows for both presentation and drawing objects?

Correction: f11, not f5. The formatting dialogue window cannot change the font for all descendants of an object such as 'outline'. There seems to be no ability to change the default font.