screen time password

If you know the Screen Time password, you can certainly change it. What you didn't say is if you've forgotten your Screen Time Passcode. If that is the case, as long as you have been backing up your iPhone, you will have to erase the phone, then restore your data back (but not from backup, or you'll be right back where are). If you haven't backed up your iPhone, you will lose your data.

So, have you forgotten your Screen Time Passcode or do you just want to change it?

I'm going to assume you have forgotten your Screen Time Passcode and if my assumption is correct, erase the iPhone using your home computer with iTunes, by following the directions in this link:

If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

Then you will have to use the link I provided and erase your device using your home computer with iTunes.

You should write these vitally important codes and ID's down somewhere for easy recall to avoid having to go through this painful process.