Edit theme structure

Need help please.

I want to make changes to my theme’s structure. The logo is currently placed in the ‘main-header’ as per default theme design – I want to move the logo to the <div class=”row”> in the ‘top-header’ BUT DONT KNOW HERE TO DO IT!

When I open ‘Inspect Element’ it works nice because I can edit the html code in there but obviously it doesn’t write to the file server. Where do I edit the html/page/theme structure? I’ve added images etc but that was in the css code.

Help please?