Verified answer

On a Nikon DSLR, pull up the image on your lcd review screen, and then press the "waste basket" button. The camera will ask you for confirmation.

If you can tell me the model, I can be more specific.

To delete "some" photos can accidentally lead to deleting "All" photos (and when that happened to me, I thought I had a heart attack). Since you did not state the model of you camera, it's probably best to study the manual (as this is a very basic function) rather than us guessing what button to press. But again, if you run low on space, get a new, larger memory card, and when you have to delete something, you can do that to ALL the photos, not just one or two, and by chance, choose "delete all" instead.