How to replace Site Title with image

Hello, I'm a lot of a newb with CSS and I would like to know how to replace the site title and tagline with an image. The site is here: http://www.snekkeren.co.uk/ And I want the top left title and tag line replaced with this image: http://www.snekkeren.co.uk/wp-content/uploads/2017/07/NoBckGrnd_Logo.png I may tweak the image, but I can handle changing the image once I have the right code and where to put it. I've tried playing with various options from other help threads for other themes, but dunno what I'm doing wrong. Assume I know nothing! Cheers, Rohan