Probably the most drastic of the suggestions on this list, a full restore requires you to fully and completely reinstall your iOS. Before considering or performing a restore, be sure that your device has recently been backed up. This way, you will not lose any information currently stored on your phone.
To check when your phone was last backed up, visit:
Settings
iCloud
iCloud Backup. Here you will see the last successful backup date.
You can click Back Up Now to start backing up your device to iCloud.
