After updating an iPhone, maybe it’s stuck. Doesn’t happen much, but it can happen. When it does, it’s great if you’ve got a backup of your phone. And those traditional means of restarting, resetting, and restoring don’t work any more. Or at least they do, but they’ve moved.
If you need to DFU or restore your device, starts by plugging the phone into a computer running iTunes. Then press and hold the power button down for 3 seconds and press the volume down button while you’re holding that power button. Hold both down for about 10 seconds and let go of the power button, holding the volume down button for 5 more seconds.
This process is pretty specific and I’ve often had to do it 3-4 times to get it just right. If you see the Apple logo at boot, the device is just rebooting (and that’s usually all I’ve needed). But if you really need it to go into restore or DFU-mode, you’ll want to see the screen that says Plug Into iTunes. Once you see that, you are in restore mode. If you want to be in DFU mode, you’ll want it right in the middle, where the screen is black.