How do you manually reset an iPhone 4?

That depends on what you mean by "manually reset." There are a few different methods of "resetting" your phone in various ways:

* Go to your Settings app and go to General, Reset. You can choose various kinds of resets here, including resetting your network settings, erasing all your settings, erasing all your content AND settings, and so forth. * You can power your phone off by holding down the top (sleep/wake) button and sliding your finger across the red "slide to power off" bar until the phone powers off. Power it back on about a minute later by pressing down on the same button until you see the Apple logo. * Perform a hard reset by holding down both the top (sleep/wake) button AND the home button until the phone shuts off. Keep holding until you see the Apple logo, then let go. * Perform a Device Firmware Update (WARNING: WILL ERASE EVERYTHING ON YOUR PHONE) by holding the top button and the home button until the device powers off. Let go of the top button a few seconds after the phone screen goes black, but keep holding the home button. Plug the unit into a computer with iTunes to restore the device from recovery mode.