1. Hover over the image you want to delete
2. A grey box will appear around the image and a trash can icon will appear in the top left corner of the image
3. Click on the bin icon that appears on top of the image - the grey box will turn red
4. Click on the "Publish" button at the bottom or top of the page
5. The selected image is deleted
PS: if you want to delete all the images you have added (from the gallery), click three times on the trash can icon that appears on one of the images and click the "Publish" button at the top or bottom of the page.