Take note, below steps can spolied or malfunction and lost all your data.So, test is as your own risk and any lost of your iPhone is not my responsibility.
To do the updating task, you must be completed before requirement.
- Download iOS 6.1.4 for iPhone 5
- Download iOS 6.1.3 for iPhone 4S and lower model.
- Download iOS 7 beta 1
- PC must be downloaded and installed latest iTunes software
- Make sure you had been full backup your iPhone before proceed the updating process. (Warning: This is a must step to avoid lost of all your data)
OK. Let's start the show.
Step 1: 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 2: Once the device has restored make sure to setup as new and that you get to the home screen.
Step 3: 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.
Step 4: Once iOS 7 is updated, just click Restore Backup under Manual Backup and Restore. iTunes will ask you to choose new backup or old backup to restore. You have to choose the old backup that you did full backup before restore to iOS 6.1.3 as new phone and updating iOS 7.
You will see your iPhone is updated to iOS 7 with all your data when restore task completed.
I've tested with iPhone 4S to write this post.
May you all be happy.
(Be knowledgeable , pass it on then)