Banners can be added to your online store via the Design section, (which will appear on your home page) or can be added to your collections.
If at any point you need to delete or replace banners, simply go ahead and:
1. Click on the banner so it becomes green
2. Click on the settings cog seen in the top right hand corner of the banner
3. Click on the 'trashcan' icon seen in the bottom left hand corner
4. Click save changes.
That's it - your banner has been deleted.