can we update apple iphone thru a pc

Yes, as long as it has a compatible version of iTunes installed.

While you can do that, a Microsoft Windows system or a Mac is no longer necessary:

"With iOS 5, you no longer need a computer to own an iPad, iPhone, or iPod touch. Activate and set up your device wirelessly, right out of the box. Download free iOS software updates directly on your device. Do more with your apps — like editing your photos or adding new email folders — on your device, without the need for a Mac or PC. And back up and restore your device automatically using iCloud." - per Apple