Changing logo image and making link to portal
 

Pardon my ignorance but can anyone in simple terms please explain this newbie how to make our site logo image and banner appear at the top of the page and make it have a link to the portal?
It all worked fine in 3.6.2, but upgrade to 3.8.5 broke it.

I noted a sticky item in the forums referring to changing code in 'the header style' Where can I find this and how do I change it? Is this possible from the menus?