Header code

I’ve been tinkering around with this theme lately, testing it on my localhost before moving it to my actual site. One problem I’m having is trying to edit the header code. Unlike my current theme, I can’t seem to find the HTML code for it anywhere.

I basically wont to remove the Text (site title/name) in the header, and replace it with an image. And I need to see the code for it. The only thing I can find in the header.php file is this, education_zone_site_header();.

This looks to be a function that undoubedtly has the code somewhere else. So I want to know where exactly I can find that file so I can edit it.