I see that you've inserted that image in Appearance -> Background with the following options:
* Position: Right
* No Repeat
* Attachment: Fixed
* Background color: #91BEC1
My best — and most simple — suggestion is to create a new image in an image editor (sized 1280 pixels wide, with a height of 149 pixels according to this image), with that logo inserted on the right side of it, while keeping the rest of the background transparent.
Then, upload that new image in Appearance -> Header, making sure to uncheck "Show header text with your image".
Note that the Able theme is responsive, which means it can resize the content according to the size of the browser window, so this might not work properly.
So, with the Custom Design upgrade (included with the Value Bundle), you can edit the CSS in Appearance -> Custom Design -> CSS so the header image will be located along the right side of the header. (This will likely be your best bet.)
You can feel free to post in the CSS Customization forum if you'd like to go that route.
Let me know how you proceed. :-)