To remove a picture from the Roll, hover over it and point to the checkmark button . As it changes to , click the button.
To remove a collection from the Roll, hover over a picture that belongs to the collection you’d like to remove, and then click Open in Collection . Now, point to the checkmark button next to the collection title and, as it changes to , click the button.
If you’d like to see the picture on your display after a while, you’d better add it to Favorites. Otherwise, you may need to spend some time trying to find it again.