How do I install iOS 16 on my iPhone 7?

You can't. iOS 15.8.4 is the highest version you can run on an iPhone 7.

If you need to run a,higher version, you will need to purchase a newer phone.

An iPhone 6/6 plus can't be updated beyond 12.5.7, it doesn't have the hardware required to run anything higher.

If you need a higher iOS version, you will have to purchase a newer phone.

• If you have an iPhone 6S through 7, or SE 1st generation, you can update to 15.8.4

• If you have an iPhone 8 or X, you can update to 16.7.11

• If you have an iPhone SE (2nd generation or later), or XR through 16, you can update to 18.6

Probably you are seeking to update becuase --> New Apps that require higher iOS versions than your device can be updated to... - Apple Community