How can I updates my iOS to 14.0

If yours is a 6S, you should be able to update using the directions in this link...

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

You said......iOS14 is no longer available. It has been superseded by iOS15.5. But you need a phone newer than iPhone 6 to be able to update to that version.

This was not correct, and frazzm737 never said that the 6s could be updated to 14.

If you have an iPhone 6S, and you update the software, it will be automatically updated to iOS 15.5.......not iOS 14.x

iOS14 is no longer available. It has been superseded by iOS15.5. But you need a phone newer than iPhone 6 to be able to update to that version.

The OP says that it is a 6S which can be updated.

6s can be updated to 15.5.

Yep…..but to 15.5, not 14.

Yes it was.

….and still is!