If you’d like to add a logo click on “Pages” and then open up your event site. In the header you can then choose to have a logo instead of a titel.
Preferred format is 4:3 and size above 800x600px.
If you want to keep the titel but still use your logo you can add the logo to the picture you are using for the background photo.
Also remember you can add your logo to the "Organizer" block if you want to do that instead.