To delete some of the images/files that aren't being used by the website, follow these steps below.
1. Go to Content - Media Manager
2. Find the Image/File to delete and hover the mouse over it. Click on the trash can icon to delete or "Erase" the image:
3. Click "OK" to finish deleting the image.
The image/file will be deleted from the site and it will not take up any space/bandwidth .