When you log in to OpenSolar for the first time or if you haven't uploaded a logo yet, you will see an Upload Logo button in the Header of a specific project in Projects, or on the MyEnergy and Control sections.
Note: The upload logo button is not available on mobile screens.
To edit your company details including logo, you can go to the Business Info section in the Control page.
The video below will guide you through the whole process of setting up your Logo and Business Details.
See this Article for in depth steps on setting up your Business Details.