Changing fonts for all text

Text styles are defined in Format -> Style -> Text styles (the last item on the list on the left). This will probably not work if you've manually changed (overridden) a font somewhere, so in this case you can try the Format -> Reset text style overrides command (careful as it could potentially reset more than what you want). Finally, another thing to try is to automatically select multiple texts by right-clicking a text you want to change (e.g. a Title) and then clicking Select -> Similar or Select -> More... on the context menu that will appear. Select -> Similar could potentially select more things than what you want so use Select -> More... instead to refine the selection. Once you have a good selection, use the Properties panel to change the font. Repeat for any other texts that were not processed previously.