(Premise: licensed or Hong Kong version) Quit looking for my iphone, connect the computer itunes, plug in the USB on the back of the computer, back it up first, and click Restore. If you don't approve, hold down the On/Key +home key at the same time, wait for the machine to restart, then connect to itunes, hold down shift on the computer keyboard, and click Update or Restore on itunes at the same time. This will refresh your system. If you choose to restore, you need to download the firmware of iphone first. If you choose to update, itunes will automatically download the highest version currently available for your iphone.
Remember: if you can not upgrade in the future, you will not upgrade;
good luck