Step 1. Visit page that you want to edit.
Step 2. Click 'Edit' (near top-right of page):
Step 3: Click 'TITLE/BANNER OPTIONS'
Step 4: Banners can be added via either Quicklinks OR via TEXT/Image blocks within the page.
How do I make the image fit the full-width of the page?
Under the 'Advanced' section for the entire 'ADD HERO BANNER / CAROUSEL TO PAGE' block (not the 'Advanced' section for the individual banner), check the 'Set all images full-width' option:
You can then save/publish the page.
Note: You can also add quickinks to banners.