How to update my iPhone 6s

Start here: https://support.apple.com/en-us/HT204204. If you really are on iOS 13, you will need to update through your computer to get to iOS 14.6.

Your phone can be updated to the most current iOS (14.6).

It has been announced that it will also be supported in iOS 15 as well.

Instructions to update are here:

https://support.apple.com/en-us/HT204204