How to reset or clear off a iphone 4?

I upgraded my phone and am giving my old iphone 4 to a friend of mine but I want to clear EVERYTHING off before hand. I don't know how to reset, restore to factory settings, or clear it, how ever you would label it. Yes I know how to remove my apps, therefore removing anything to do them. But I have had pics, videos, text, and such that I have delete but I want to be sure there's no way she will have access to them. So how do you go about wiping it clean or restoring it to a blank phone?

How to Erase Your iPhone's Data Before You Sell it

http://netsecurity.about.com/od/iphoneipodtouchapps/a/How-To-Erase-Your-Iphones-Data-Before-You-Sell-It.htm

Go to Settings - General - Reset (at the bottom) - (select) Erase All Content and Settings.

This will erase everything from the phone and return it to pre activation mode. The phone will be blank.

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