You can add Logo files in the Basic Setup. You can also upload there Logo Reversed that can be used if you have some pages with dark menu or transparent menu for better readability.
To change logo size in the menu you will need to edit each Layout you use.
Layout = header (menu) + <page-content> + footer
You can do it directly on your page (e.g. “About us” page and most of other pages us “Dark Menu Layout”) this way:
or you can select it via /wp-admin/ panel this way:
Edit Menu and change logo size
e.g. to 70
to change tablet / mobile size please change it this way
Click Update to save changes
If your website use more than one layout and you wish to migrate menu (e.g. some homepages and blog page use by default transparent menu layout) please edit other layout and change it same way again: