How to upgrade my iPhone 6s to 15 IOS

Go to Settings > General > About

What does it say for iPhone Model and Software Version?

You need an iPhone 6s/6s Plus or newer in order to run iOS 15..

Supported iPhone models - Apple Support

If your iPhone is really an iPhone 6, then you cannot upgrade beyond iOS 12

have you read thru this support article for updating?

Update your iPhone, iPad, or iPod touch - Apple Support

need more storage for update?

If you need more space for an update on your iPhone, iPad, or iPod touch - Apple Support

issues?

Updating iOS: common issues and solutions - Apple Community

video..

Update it from a computer or through the Software Update function in Settings.

If it's currently on 12.5.5 or offers to install that version, it's not an iPhone 6s and isn't capable of 13 or above.

(209510)

THBLady Said:

"How to upgrade my iPhone 6s to 15 IOS"

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Use a Computer:

Try my User Tip: Update your iPhone Using a Computer