How do I update iOS 16 on iPhone 6s?

Sorry but your iPhone 6s no longer receives the latest iOS software updates and cannot be updated past iOS 15.8.3. You will need to purchase a newer iPhone, at least an iPhone XR to run iOS 17, and ideally iOS 18. Personally I would suggest you purchase an iPhone 15 Pro or later that supports Apple Intelligence.

Again … iOS 15 is as far as your iPhone 6s can be updated.

iam Poor man

Irrelevant, being poor isn't going to change the fact that an iPhone 6S doesn't have the hardware needed to run an operating system higher than iOS 15.8.3,

Same answer, an iPhone 6S cannot be updated beyond iOS 15.8.3.

Not possible.