[list_item]If you are not already registered to iOS development Centre, then simply click on http://developer.apple.com/programs/ios [/list_item]
[list_item]You must have an Apple ID for the process to go forward. It costs $99/year if you’re in the United States, or £60/year for those in the UK.[/list_item]
[list_item]After signing in, you will have to register your device’s UDID on the developer’s portal. Once you have the UDID, navigate to http://developer.apple.com/account/ios/device/deviceList.action in your web browser, give any Name to your device, insert the UDID and hit Continue to register your device. [/list_item]
[list_item]Next Step is to simply download iOS7[/list_item]
VIDEO Guide on : How To Install NEW iOS 7 Beta 3 (FREE) Without A Dev Account Or UDID
if there is problem or you are unhappy with iOS 7 , you downgrade it to iOS 6 . here is video help with complete guide.