Iphone 4 - Cannot download IOS 6

My apple Iphone 4 will not download the IOS6 software update. When I go to "settings" then "general" there is not a "software update" between "about" and "usage". I was just given this phone by a family member for one of my kids. This is a bit strange that there is not a software update area in the general tab. The latest software on this phone is 4.2.10. Help!