There is a support page where you can see with the help of images how to remove or save the pictures from the storyline (the main function of the Snapchat) application. Access the page to see how to remove the images. Basically, you have to click on a story or images you have posted, then tap on the X and that's it. The image/story will be removed.
To find out more about this procedure, access the official website: https://support.snapchat.com/a/delete-story