I won’t my phone to be updated

You did not say which iPhone you have but in general, here is what you should do. Select Settings > General > Software Update. If your iPhone is eligible for an update, you will be prompted to do so. If you have questions regarding this, please reply, letting us know which iPhone you have and what its current iOS is. If there is a problem, then tell us what any error message says. We want to help if we can.

Update your iPhone or iPad - Apple Support