How to update iphone 4 ios to newest?

I know the update for the iphone came out several years ago but I never got around to it. Now, whenever I try to update it (even plugged into my computer and with Wi-Fi) I'm not given the option to update. How do I update my phone?

Go to settings>general>software update

The latest iOS version you can get for the iPhone 4 is iOS 7.1.2. Follow Jimmy's suggestion, or you can do a restore in iTunes.

You'd have to download that update (iOS 7.1.2) from a site that offers it, iClarified.com is one & then install it that way. Look up manually installing iOS.