You won't be able to...
ios 10 requires an iPhone5 or newer.
You can't update it to iOS 10, you can only update it to the current version i.e. 11.3 . To do that go to Settings > General > Software Update or do it via your computer's iTunes : Update your iPhone, iPad, or iPod touch - Apple Support
Question: Hello dear . I can not update my phone ios 10 what van i do? My phone is iphone 4s