Not knowing which way you are trying to update. It takes around 5-10 minutes when my 5s updated over the air.
After the update the screen goes black. You simply touch the power button and it should be OK.
However I am not updating through iTunes. I have read of problems via that method.
Go to http://www.apple.com search under support communities to find a solution.
Usually holding down the power button and the system menu button (large button on bottom of iPhone) together will force