You will taken to the thumbnails page, where you will see a preview of every image in your current gallery. Find the image you wish to remove, and click either the "Disable" red circle icon or the "Delete" trash can icon from the list of icons underneath the corresponding image.
Disabling or deleting an image from your gallery prevents members from being able to see the images in question. However, disabled images will not be deleted from your database. If you disabled an image, you can click the "Enable" green plus sign icon to restore that image to your site.
Deleting an image, on the other hand, will permanently remove the image from your CARMA database. Thus if you wish to prevent an image from being viewed by your members but do not want to permanently delete it, you should instead disable the image.