To Edit your Organisation profile, first access your Admin Dashboard.
Next click on the Engage > Profile tile
This will take you to your Organisation Profile. You will see an "Edit Profile" button on the top right of the banner image. Click that to edit your profile.
Edit you organisation details, and click next at the bottom of the page to get to the page where you can change your banner image or logo.
If you wish to delete you organisation profile click the "Archive" button