So what I did was open up the Settings app, scrolled down to General, and then kept going until I saw something called Transfer or Reset iPhone — it’s right at the bottom. Tapped that, and then on the next screen, there was this option that said Erase All Content and Settings.
Once I hit that, it asked me to punch in my passcode, and then I think it also asked for my Apple ID password too — probably just to confirm it was me before it actually started wiping everything.
Once you confirm, it’ll start wiping the phone. Everything gets deleted — apps, photos, settings, everything — so make sure you’ve backed up anything you care about before doing this. I used iCloud for mine, just to keep things easy.
Also, double check that Find My iPhone is turned off, or at least make sure you remember your Apple ID login. Otherwise, whoever uses the phone next won’t be able to activate it — even you.
The reset itself only took about ten minutes. After that, it boots up to the “Hello” screen like when it was brand new. You can set it up again from there or just leave it as-is if you’re selling it or giving it away.