How do I update my phone

If your tag line is correct and you own an iPhone 7 which is on iOS 15, you cannot update to iOS 16 or iOS 17. The phone is too old and lacks the hardware required to go higher than iOS 15.8.2

I wanna update my iPhone but it takes me to this

We cannot see your iPhone, so we don't know what "this" might be. Can you post a screenshot or provide the exact text of the message that you see?