The content for your alert is edited under Content > Section > Alert Popup.

You can add any kind of text, links, or buttons in the "content" field. Assign the image you'd like to display via the "backgrond image" field. You can swap out the alert's content anytime you need to!

In the Alert Popup section, check the "hide popup" option to hide the alert from your site, and uncheck the box to put it back on your site!