You may need to reset your device. Before doing so you should create a backup. Create one by opening the Settings app, then select iCloud. Sign in to your Apple ID and tap Backup. From here tap Back Up Now. Once the backup is complete return to the main Settings menu and tap general followed by Reset. Here select Erase All Content and Settings. This returns the device to factory settings. You will then have to follow the setup process. At a certain point select Restore from iCloud Backup and sign in with your Apple ID. Once this has finished then everything will have returned to default.