How do I know when my iPhone is updated

Select Settings > General > Software Update. If your device is eligible for an update, you will be prompted to do so. Otherwise, you will se a message that states - iOS is up to date.

Assuming you have a compatible device, see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support

If the above Apple articles do not help, please post back with relevant information.