Deleting Files from iCloud
The simplest way is to log into iCloud on the web from your Mac or Windows device. Navigate to the NP Risk folder in iCloud. Select the file(s) you want to delete and then tap the Trash icon. You'll be asked if you want to remove the files from all of your devices. If you do, click OK and go ahead.
If you want to watch the process, turn on Airplane mode for your devices except your Mac or PC. Delete the files with your web browser as described. Log out from iCloud on the web, and turn off Airplane mode on your devices (one by one if you want to check). You'll see the files disappear.
Files created locally on your device when iCloud was turned off are not affected and you can still use them on that device (but not on other devices connected to iCloud).
Deleting Files from a Device (not in iCloud)
Delete the app from your device. On the Home screen, tap and hold on the app icon. The icons will all start to jiggle. You'll see an X in the top left of each icon. Tap it to remove the app and all its files from your device. When you're done, tap Home to stop the jiggling.
When you redownload the app from the App Store or iTunes, it will have the default data and, if iCloud is turned on, your iCloud files for that app.
This works the same way for all apps and their local files.