Welcome to the community If the pictures are saved on Google+ with instant upload then technically they aren't on your device so to delete them you would need to go on the computer and delete them. Otherwise have you tried long pressing the photos to delete them? Hopefully this helps if not get back to me.
Hello avlntom1 and welcome to Android Forums. I hope you enjoy your time here and that these forums serve you well. Thanks for joining our community. Enjoy..
