The following tutorial covers changing of Flow diazo Theme logo on a Plone 4.1 website.
Flow Plone Theme uses default Plone 4 logo, displayed at the left top left area. Its width is 215px, and hight - 56px.
You can replace this logo with yours via ZMI. Open portal_skins -> sunburst_images folder, there is logo.png image. To set your own logo press Customize button:
Press Browse button to select the your own logo. Click Upload:
Now you see your new logo.png image, and it is automatically put into custom folder:
Now when you return to Plone interface, you'll see new logo image (Quintagroup logo):
For the subsequent logo replacements go directly to ZMI portal_skins/custom/logo.png and upload new logo image here.