your self-recorded iOS videos are not accesible . Neiter to delete them nor to watch them.. they are just part of the full iOS backup at once. To delete your backup ( which is a bad idea ) , open Lions icloud preference in Systemsettings, click on the space indicator "manage". From there you can delete cloud data.
If you thought of purchased itunes videos : they are in your purchased items list and do not take up your space. Apple holds them for you.