Rather watch this on video? View the explainer here: Changing the Cover image on a Buzz.
You can edit the cover image of your Buzz (provided you are an Owner or Author of the Buzz) by clicking on the ‘Edit Cover’ button .
A cover image is always scaled and cropped to fill the entire area available to it. By default, a cover image is aligned vertically centered, but sometimes this might mean the important part of the image is cropped out - to align the image off the top or bottom, change the vertical alignment settings .
You can choose to turn the cover image on a Buzz off by opening the Settings panel  and setting Cover Image to ‘Off’ .
View the video explainer here:Changing the Cover image on a Buzz.