The new iPhone software will then begin to install on your phone. iTunes will display a progress bar that says "Updating iPhone software."
Do not disconnect your phone during this process.
After the software has been installed, you'll see a message that says "Verifying updated software." This process takes just a few minutes; do not close iTunes or disconnect your phone while it's running.
Next, you may see a message that iTunes is updating the iPhone's firmware. Let this run; do not disconnect your iPhone while it is doing so.