I want to update my software

Here's a simple and fast way to see what is possible with your device without having to identify your exact model. It will also make sure you are running the absolutely newest iOS your device can support.

On your device, tap:

Settings > General > Software Update.

1. If it says your device is up to date there is nothing more you can do. If apps you are trying to use say you need a higher iOS version, you will need to buy a newer device if you want to run those apps or features.

2. If it says an update is available you will only be given one update selection which will be the highest available iOS version supported by your device. Click on a link below for full instructions about how to update with wi-fi or 5G, or using a computer if you have storage or connectivity issues. If the update listed is not equal to or higher than the iOS version you need to use a feature, you again will need to buy newer equipment if you want to use that feature.

"Update your iPhone, iPad, or iPod touch" click here --> https://support.apple.com/HT204204

Or this video:

"How to update your iPhone or iPad" click here --> https://youtu.be/csJAEyvvruY

If you try to update your device and it says that it is up to date and is on iOS 12.5.4, then you have an iPhone 6, not an iPhone 6s. The iPhone 6 will not update past iOS 12.5.4, it cannot support it.

How to update my iPhone 6s?

Use the instructions provided in this thread.