1. From the Storyboard, tap the Gallery page that you would like to edit.
2. Tap the media icon to bring up the Media Picker.
3. The Media Picker will open for you to make a selection.
If your "Photos" and "Albums" tabs are empty, you need allow the app to access to your device photos. For instructions, see this article.
4. Upon tapping to a select a new image, it is added to the page. Next, tap "Done".
Tapping multiple images will add all of them to the page (up to 6).