You can add or change your custom image logo inside of the SpaceCraft Dashboard, here is how:
1. Select Design from the Dashboard navigation bar.
2. Under the Sitewide section in the righthand Design panel, select Header & Logo.
3. Select and Upload your image/graphic logo in the blue upload box.
4. Under Sitename, choose one of over 100 Adobe TypeKit fonts and style the text name of your website.
5. Select Save and Publish to make it live now.
Note: When you upload a graphic logo, you can change the size and alignment of it, as well as include/exclude the Sitename.
You may want to change your actual sitename, see here: How do I change my Sitename?