Read the following tutorial and learn how you can change a logo in Domino Plone theme.
Domino diazo theme comes with the default Plone logo.
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.
Now press Browse button to select the logo image you want to upload from your computer and click on Upload.
New logo.png image will be automatically put into portal_skins/custom folder, which means that for the subsequent logo replacement you should directly go to custom folder and upload new logo image there.
Now when you return to the Plone website, you'll see new logo image.
To change slogan please go to Site Setup > Theming > Advanced settings tab. There in Parameter expressions insert the text you need.
slogan = string:Theme for Plone