There's a video somewhere on the GD site for that, but it comes down to appearance > editor > patterns > all patern parts > header.
Once you have the header-template on your screen on the left to the top there is a hamburger-menu. Click that once, and you will see a text BS Navbar. Click that once on the small arrow next to it, and you will see (probably) menu-wrapper. Here also click on the small arrow and you will see BS Navbar Brand.
That's where the magic goes. Click on it and to the right of your screen you see under content text, icon and link.
Text: erase it.
Icon: here is where you upload your logo
Link: here is where the logo has to link to. (if not to the homepage).
Please note: on the width I have 277px as when it is bigger it distorts the menu on mobile versions.
I tried to have a logo full width above the website but did not find how to do that. (I should ask support but am stubbornly trying to figure it out).
You can take a look at https://briefondernummer.nl to see how my logo looks.
If you ask support I am sure they can send you the link of the video. That's how I picked it up anyway.
