How do I make logo secure under https?

I’m adding a contact form on a post ( https://www.thelittledoglaughed.org/2014/05/21/star-team-test-prep-series/ ) and want to have it come up without warnings under https. Right now I get the warning about the page containing insecure elements. I think it’s the logo, but I can’t see where I can change how it’s called. Any suggestions?

Thanks,
Linda