Method to manually do a software update by iTunes app on an iPhone?

And what to deleat from the iPhone before doing the update? How much time will it take to update? One night maybe? While the iPhone is charging?

Itunes is normally automatically updated automatically from the app store or during an IOS update. No user intervention is needed and it happens in the background. If you want to do manual update, go to the app store, updates, if itunes app needs updating it will be listed