The following tutorial covers changing of Uni Theme logo on a Plone 4 website. Instructions for diazo Uni theme - see in How to replace diazo Uni logo in Plone 4.1 tutorial.
Uni Plone Theme logo is displayed at the top left area.
You can replace this Uni Theme logo with yours via Zope Management Interface. Go to ZMI interface: Site Setup -> Zope Management Interface -> portal_skins -> uni_images folder. You will see uniLogo.gif image:
This is a default Uni Plone Theme logo image. To set your own logo press Customize button:
Press Browse button to select your own logo. Click Upload:
Now you see your new uniLogo.gif 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/uniLogo.gif and upload new logo image there.