How can I update my iPhone 13 Pro Max to the latest iOS version?

Assuming you have a compatible device, see: Update your iPhone, iPad, or iPod touch - Apple Support

And: If your iPhone, iPad, or iPod touch won't update - Apple Support If the above Apple articles do not help, please post back with relevant information. 

Hello~ Click on below…

Update your iPhone or iPad - Apple Support

If there are common issues…

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

What happens when you try to update?

~Katana-San~

Your tag line says you have an iPhone 13 Pro Max running iOS 17.

If you are trying to update to iOS 18, it is not available yet.