The more you use Reports+, the more space it will occupy on your device - just like any other mobile application. You shouldn't worry because of this. Your application will check the storage area in a synchronized way with your device’s operating system after some time. If the space Reports+ uses still bothers you, you can delete application data on Reports+ > Settings > Delete History tab.
As the second option, we recommend you to delete the app and install it again.
In order to see how much space Reports+ occupies on your phone:
iPhone & iPad:
Go to Settings > General > Storage > Manage Storage and then find Reports+.
Go to Settings > Applications > Application Manager and find Reports+.