Want my iPhone to be updated
Can you update my phone
iPhone 6s, iOS 12
If you indeed have an iPhone 6S as your tags suggest, you can update by connecting to WiFi (not a hotspot), then going to Settings > General > Software update.
If that fails, you can use a Windows device running iTunes or a macOS device with Finder to update.
If your device is actually an iPhone 6, you will not be able to upgrade past iPhone 12.5.6.