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1. Go to your Course page, then on the left hand menu, Details & Actions , menu select "Edit display settings" (see image below).
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Also, you can conveniently select "Stock images from Unsplash". These are images that are already created on the platform for users. By default, images that initially show are based on your course title. However, you can use the "Search" box and find specific images you want. Once you click on the image you desire, then select then select "Next" at the bottom right of the Insert Image dialog box. Adjust the portion of the image you want to be visible on your banner, then select "Save".
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2. Alternatively, on the Course page, you can access the banner from the left hand menu by clicking the "Edit display settings" under Details & Actions (see image below). You can also access your banner by hitting the pen 
icon on the far upper right on the existing banner (see image below).
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Removing Course Banner
Repeat step 1 or 2 in "Ways to Access Banner for Editing Purposes". Under the Display Settings dialog box you will note that the Course Banner is toggled "on". If a course banner is not desirable then toggle to "off" and then click on the "Save" button at the bottom of the dialog box. You also select select the delete button 
at top right of the Display Settings dialog box.
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