Change body font

It’s in /duena/bootstrap/css/bootstrap.css -and- /duena/css/editor-style.css

You should consider creating a Child Theme for your modifications to avoid losing your customizations during a theme update.

OK, now I have problems with featured images/thumbnails – it looks like this ??
https://www.dropbox.com/s/40auwgqfmutglay/aaaa.jpg

I’m afraid I have no suggestions on that one.

you can use a plugin called “Font” that is very easy to use.