As per Apple Documentation,
When a user downloads an app update, iTunes installs the update in a new app directory. It then moves the user’s data files from the old installation over to the new app directory before deleting the old installation. Files in the following directories are guaranteed to be preserved during the update process:
/Documents /Library Although files in other user directories may also be moved over, you should not rely on them being present after an update.
But I am developing an application, and using iTunes for installing the application, all the existing images and files are getting removed on synching device with iTunes.
Also while synching app with iTunes, it is showing Copying ${PROJECT_NAME} in device, whereas it should be updating.
So, if the user is updating any application from AppStore in Mac machine, and is synching the device, will all the records saved in Document Directory for all applications will be removed and user will require to save them again.