What Happens If You Reset Your iPhone?by Tom Ianello ; Updated September 01, 2017
Resetting your iPhone will return it to the state it was in when you bought it. Also know as restoring to the phone's factory defaults, this technique is useful if you are experiencing issues with your iPhone that cannot be solved through ordinary troubleshooting steps. Just remember that when you reset your iPhone, all data and user settings will be deleted and the operating system will revert to factory settings.
Backing up Your Data with iCloud
Before you reset your iPhone, you should back up your data and settings. For devices running iOS 5 or later, you can use iCloud. If you have enabled automatic backups with iCloud, your data is backed up on a daily basis as long as your iPhone is connected to a power source, connected to the Internet using Wi-Fi and has the screen locked. You can manually back up to iCloud by going to the iCloud section of your Settings menu, selecting "Storage & Backup" and tapping "Back Up Now." ICloud will back up any iTunes content you've purchased and gives you additional storage for photos and videos on the Camera roll, device settings and account information, app data, home screen and app organization, messages and ringtones. Any music, movies or TV shows on your iPhone that were not purchased through the iTunes store will not be backed up by iCloud.
Backing up Data with iTunes
If you prefer not to use iCloud, you can back up your data by connecting your iPhone to a computer that's running the latest version of iTunes, right-clicking or Control-clicking your iPhone in the Devices section and selecting "Back Up." The amount of data that can be backed up using iTunes depends on the amount of available hard drive space on your computer. ITunes will back up everything that iCloud can, in addition to content such as voice memos, Safari bookmarks, cookies, history and offline data, call history, paired Bluetooth devices and saved suggestion corrections.
Restoring Your iPhone With iCloud
After your iPhone is restored to factory settings, it will be just like it was when you took it out of the box for the first time. The Setup Assistant will provide options for either setting it up as a new phone, restoring a backup from iCloud or restoring a backup from iTunes. If you select the iCloud option, first make sure you are connected to a Wi-Fi network and that your phone is either plugged in or fully charged. After you select this option, your iPhone will restart. When it boots back up, your accounts and settings will be restored, and your iPhone will start downloading any purchased iTunes content, apps and photos and videos from your Camera roll.
Restoring Your iPhone With iTunes
If you performed a backup using iTunes, you can select the Setup Assistant option for restoring from iTunes or connect your iPhone to your computer, where iTunes will prompt you to restore from your previous backup. If for some reason it doesn't prompt you automatically, you can right-click or Control-click your iPhone under the Device section and select "Restore" from "Backup." Your data, apps and settings will be transferred to your iPhone.
Leave your phone connected to your computer during the restore process. The amount of time this takes varies, depending on how much data was on your iPhone. Be patient and do not unplug your iPhone while it is restoring. If you disconnect your iPhone before it has finished installing operating system files, you run the risk of rendering it inoperable.