It depends on who uploaded the photo.
How to delete a photo uploaded by the Business Owner
If you uploaded the photo, you will find it in the image gallery, in the Business Centre. To remove the image, hover your mouse on it, click on the bin icon and confirm.
How to delete a photo uploaded by a customer of your business (or from a user profile different from the business owner's profile)
Customers have the ability to upload photos on listings. As they don't appear in your gallery, you can't remove these images from the Business Centre.
To remove this type of picture, go to your listing, open the gallery, and click on the flag on the bottom right the image you want to remove. You will see a screen asking you for a comment; please write this: "Picture reported by Business Owner - Please decline in moderation". This will let our Moderation Team that they should disapprove this image.
Once your report is done, the picture will immediately disappear from your gallery.
Important: you need to claim your listing before you can access the Business Centre and edit your listing. This article explains how to do it.