You should always perform a backup before applying any major new firmware release. If you back up your devices to iCloud or sync with iTunes via Wi-Fi, temporarily disable both options.
To disable iCloud backup, toggle the iCloud Backup switch to OFF under iOS Settings > iCloud > Storage & Backup. To disable iTunes Wi-Fi sync, tether the device to a Mac or PC via a USB cable and uncheck the “Sync with this iPhone over Wi-Fi” box under your device’s Summary tab in iTunes.
Apple has just released the public version of the iOS 7.0 version and its a crazy number of downloads happening right now, and you cannot blame Apple for the error you are getting while downloading the iOS 7 on your device through the software update section in Settings. Here’s an error which many users have been reporting right now:
Apple released iOS 7 beta for developers. Do you want download iOS 7 and install without developer account. Done. Good news for all people. You can install iOS 7 beta without UDID.
Step 1: Download the latest official iOS for your device This will be iOS 6.1.4 for iPhone 5 and iOS 6.1.4 for all other supported devices: iPhone, iPod, iPad and Firmware/Software Download
Step 2: Download iOS 7 for your device
Step 3: Connected iPhone via USB and open up iTunes on restore hit the shift and left mouse click buttons down together this will allow you to manually search for the iOS you downloaded for iPhone 5 you would select iOS 6.1.4 for all other devices you would select iOS 6.1.3
Step 4: Once the device has restored make sure to setup as new and that you get to the home screen.
Step 5: Now on the Check for updates button hit shift and left mouse click down together this time you need to select iOS 7 for your device now when the device finishes updating it will be on iOS 7 activated.