Hello. I tried to update my phone with iOS 15.73 but still it does not update.

You do not write which iPhone you use, but if you use iPhone 6S/7/SE 1.Gen you can update to iOS 15.7.3

If you use iPhones 8 or later, you must update to iOS 16.3.1

If you are experiencing problems updating, try deleting the iOS Update file and download it again.

First, delete the iOS Update file. Go to:

Settings → General → iPhone Storage.

Find the iOS update on the list and delete it.

After that, Restart your iPhone. Then connect to Wi-Fi, and charger, and go to:

Settings → General → Software Update and try again.

Leave your iPhone in the software update menu and preferably don't use it while downloading.

You can find more useful information here:

If your iPhone or iPad won't update - Apple Support

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

I tried to update my phone with iOS 15.73 but still it does not update