How to install iOS 7 on your iPhone (selected devices) right now

While iOS 7 will not be released until September 18th , you can download and install iOS 7 today , and install it on your existing iPhone or iPad .You Can install iOS 7 on the iPhone 4, 4S and 5, the fifth-generation iPod Touch, and every iPad and iPad Mini, except the original iPad . Installing iOS 7 will give you access to exciting new features such as multitasking and improved airdrop , and complete visual check , of course , make your Apple device looks completely different .

You can sign up for an Apple developer account , which costs $ 100 per year.
to enroll in the program development. Once you register, you must add the device's UDID as a home test device, and then go ahead and download the correct image 7 for iOS device in Apple 's developer portal .

Before proceeding , back up your device with iTunes . If something goes wrong , you have to boot the phone into DFU mode and restore the backup. These images appear to be the genuine and safe to use , but have not tried them all, and of course use them at your own risk .

With its downloaded iOS 7  image (if a DMG file , you must open it and extract the IPSW ), connect your iDevice , and then open iTunes. Select the Summary tab of the device. In OS X , hold down the Option key and click Restore in Windows, hold Shift and click Restore. Select the IPSW file from the dialog box that appears, and  Your iDevice will update to iOS 7. Once the update is complete, you may need to restore your device from a backup ( and remember, you will need to update to iTunes 11.1 ) .

Source Extremetech