How can i download or upgrade ios 9 for my iphone 4s?

http://lmgtfy.com/?q=how+to+update+iphone

Hi Elbrus,

On the phone, plug your device in to power and connect to the Internet with Wi-Fi. Tap Settings > General > Software Update. To update via iTunes, install the latest version of iTunes on your computer. Connect your device to your computer. Open iTunes and select your device. Click Summary, then click Check for Update. This article goes into more detail: Update the iOS software on your iPhone, iPad, or iPod touch - Apple Support