how to add logo in wordpress Pinboard theme header?

how to add logo in wordpress pinboard theme header?

i’m trying to replace blog title with my logo, but unsuccesful so far 🙁 tried through theme options, but it doesn’t work without text underneath 🙁

any ideas anyone? i’m struggling to find what needs to be changed in header.php and styles.css

my url http://www.lucasco.co.uk

thank you!