Providing some links would help. In a short and uneducated answer, you’ll have to make your own logo and overwrite it and/or change the CSS.
edit images in your theme for example wordpress\wp-content\themes\constructor\themes\orange here
No need to hack around for this actually in Constructor!
Go into Customise and then Images, you can put an image in there and tell it where to place it, whether to repeat it etc.
I just made a 1260 x 80 or something picture (the size of the lego bricks) with a transparent background and stuck a picture on the right hand end of that:
http://mrkeefe.co.uk
http://mrkeefe.co.uk/wp-content/themes/constructor/images/physicsheader.png
HTH
