I want to get a software update to my Iphone. It is a 6S, need more data storage.

Freeing up storage space on your iPhone.

Here are some helpful articles that can guide you on how to free up storage space on your phone.

How to check the storage on your iPhone, iPad, and iPod touch

https://support.apple.com/en-us/HT201656

Manage your photo and video storage

https://support.apple.com/en-us/HT205703

Clear Other storage on your iPhone or iPad

https://support.apple.com/en-us/HT211686

The latest iOS for the iPhone 6s is iOS 14.7.1. If that is what you have, there is no update. Also, an update to an iPhone will not get you more data storage. If you do not have iOS 14.7.1, then see this for updating the iPhone. Update your iPhone, iPad, or iPod touch - Apple Support