To access the theme settings go to Network > Theme Settings.
The Theme Settings allow you to change the global styling of the theme and individual sections of the site including post types, taxonomies, header, footer, toggle sidebar and BuddyPress pages.
Changing Logos
There are three different locations for logos.
The toggle sidebar logo can be changed from Network > Theme Settings > Toggle Sidebar > Logo.
The header logo (by default only see on small devices) can be changed from Network > Theme Settings > Header > Logo.
The login page logo can be changed from Network > Theme Settings > Membership (scroll down to Login Page).