The message of the day is normally, but not exclusively positioned in the bottom right hand corner of the dashboard. For simplicity, it typically consists of the following two widgets/panels:

1. Text Panel
2. Image Panel

Editing the Text Panel

To edit the text panel, double click anywhere on the text. This puts you in basic edit mode and the text can be edited as needed:

Edit as needed. 

Submit the edited text by clicking to the right of the edit area:

Save any changes made:

Editing the Image Panel

Hover over the image panel and click on the 3 virticle dots in the top righthand corner to reveal the drop-down menu and click on Edit:

Double Click on the Image source

Enter the URL of the new image here:

Preview and select the new image. If preview does not work, check the URL, and Image type are correct. Make sure your image is in a format supported by web browsers (commonly JPEG, PNG, or GIF).

Select your image size/fill option for the desired appearance

Apply the changes and check that the dashboard has the desired appearance

When satisfied, ensure your new edits are saved.