I want to update my iPhone 6s

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. 

Talhahamdaweisu Said:

"to update my iPhone 6s"

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Update Using a Computer:

If something is available, it will install sure enough.

Use MY User Tip:  Update your iPhone Using a Computer - User Tip