FOR RETINA LOGOS VERSIONS:
To add Retina logo versions for your own logos, create retina logo, add _2x at the end of name of the original file (for ex logo_2x.jpg) and upload it in the same uploads folder as the non retina logo.
These are example steps to add the retina logo version for your custom logo.
Add the logo in theme options (name example logo.png)
Add retina version in Media. Make sure the retina logo has _2x at the end. (if original name is logo, then retina should be logo_2x)
It is important the 2 images exist in the same month folder.