Double tap the home button to bring up multitasking to reveal the row od apps below the dock, tap and hold an app icon until the app icons start to bounce, tap the red minus sign in the top left corner of the app. Closing an app clears the caching of any background images when testing content in the PressRun app. If you've made changes to something in the background layer and the changes don't appear close the app and relaunch. Also a good way to boost battery life.