Replace title with logo in header

Hi everybody!
I’m trying to understand how to insert a logo instead of the usual text in the header of my Yoko site. I already deleted the default header image, but I can’t figure out how to fix this problem.
The theme is personalized using a child theme, here’s the header.php of the child: http://pastebin.com/ZMrCp0ka

It seems that the thing I should change is the header.php file, because there’s nothing relevant in the CSS, but I couldn’t find the code I should tweak.

Thanks for reading (and hopefully for helping!)

the site is hookii.it