You can add your own logo to the report in the report builder view. Simply select the report you need in the home screen, and click on the three dots and select edit.
Click on Whatagraph logo in the report header to access the settings.
You can upload the logo using the menu to your right. Please note that logo has to be a PNG file (500 X 100 px).
Tip: Use your mouse to zoom in or out on your logo.