I want update my iphone

To update to the most recent, compatible version of iOS 12.5.7, please 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. 

I want to update my iPhone 6s

yammah wrote:

I want to update my iPhone 6s

No matter which version you wish, the process to update is the same as posted above.