From the Dashboard Hover over Settings Click on Theme Customizer

Change_Header

Click on Header & Navigation

theme_customizer_-_Header_&_Navigation

Here you can change all parts of the Header
Header_&_Navigation

To Change the Logo or your organization name Click Site Logo & Title

Header_Site_Logo_&_Title

  1. Remove the Image
  2. Change the Upload – allows you to upload a new image or choose from those in your media library
  3. You may type your Organization’s name here if you would like it to appear in the header.
  4. Change the size of your header text.
  5.  Click where it says select color to change the color of your text for the header.

More information about the other header features and site navigation can be found here http://www.elegantthemes.com/gallery/divi/documentation/customizer-header/.