Too excited to wait for iOS 7? It is possible to download and install now, but you have to be a developer to do so (legally, anyway).
Apple is expected to release the next major update to its mobile operating system, iOS 7, in early September, with the final build to developers anticipated for 5 September and the public release on 10 September (these dates are not confirmed). Right now, though, app developers — and anyone willing to pay $99 (£63) to register to become an app developer can get their hands on the beta, known as iOS 7 beta 6, right now. I'll outline the steps for how to install it below.
If you're not willing to register as a developer, the way to get iOS 7 beta 6 would be to grab a copy of the IPSW file containing the code (build 11a4449d) — and let me note that doing so would not be considered legal.
In any event, here are the steps for installing iOS 7 beta 6. Note that if you already have a previous beta build of iOS 7 installed, you can update the software over the air and don't need to go through all these steps.
1. Backup your device
I always recommend backing up your device (either to iCloud or to your computer) prior to a major software update.
2. Update iOS and iTunes
Check that you have the latest versions of iOS and iTunes. For iPhone 5 owners, it is iOS 6.1.4; for older iOS devices, it's 6.1.3. For iTunes, the latest version is 11.0.5.
3. Download the build
Download iOS 7 beta 6 IPSW from Apple's Dev Center for iOS. We do not condone downloading unsanctioned/illegal builds of the iOS 7 beta, but of course, they exist.
4. Connect your iOS device to iTunes
Plug your iOS device into your computer. In iTunes, navigate to the device on the left rail.
5. Install the file
In iTunes, hold down the Alt or Option key, and in Windows hold Shift while clicking "Restore your iPhone/iPad" with the iOS 7 beta 6 file.
Some users have reported that non-developers can hold down the Option key or Shift in Windows, and click the "Check for updates" button instead to circumvent the verification process of the UDID (which if you are attempting to install an illegally downloaded copy of the iOS 7 beta, you'd need to do).
Please note that I have not personally verified whether this works and don't condone it. If you do try to go this route, however, you may need to make sure the filename ends in IPSW, and strip off any other characters that may follow that file extension.
You'll see your iOS device reboot, with a progress bar filling in all the while. Be patient, because it can take a few minutes.
When the build is installed and verified, you'll see a few iOS 7 setup prompts, which you can complete to finalise your upgrade to the new UI.