How do I download iOS 15.03?

You cannot update to iOS 15.3. Your iPhone XS Max supports iOS 16 (iOS 16.4.1), so you must update directly to that version.

If you're on iOS 14 now, you'll need to use a computer to update, as it's not possible to skip a version when updating over-the-air directly from your iPhone.

You can check your current version here:

Settings → General → About

If you want to update your iPhone via a PC or Mac, see here:

Mac: Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

PC (iTunes): Update your iPhone, iPad, or iPod touch with iTunes - Apple Support

You don’t.

If you’re still using iOS 15, you may obtain iOS 15.7.5. Or (preferably) use iOS 16.

About the security content of iOS 15.7.5 and iPadOS 15.7.5 - Apple Support

Use a computer or the Software Update function in Settings to install 16.4.1. It's not possible to update to an intermediate version.

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