how can i update my itunes for iPhone 4s

Your question is not at all clear.

• The iPhone 4S runs iOS. The latest version of iOS it can use is iOS 9.3.5.
• iTunes on the iPhone is included with iOS.
• You posted in the iTunes area. This deals with iTunes on your computer, not iTunes in iOS.
• You may update your computer's iTunes as described in the article you attached ... if your operating system is reasonably current.