Why can't I update my iPhone 6s Plus?

Are you sure you have a 6s Plus and not a 6 Plus?

For a 6s Plus:

Go to---> Settings---> General---> Software-update---> Download and install the update.

You must have a stable Wi-Fi connection.

Or connect to a PC with the latest version of iTunes installed.

Charge the battery to 50% or higher.

Turn off Battery saving mode.

Don't use a Hotspot.

Don't use VPN.

And make sure you have enough free space.

For a 6 Plus...

The latest iOS version is 12.5.4

14.6 update made my new iPhone 12 nearly useless. It sucked before the update then it got worse after their update. I had to return it. The update also trashed apps that I paid for. Now they come up with advertisements and missing features. I should not have to pay for apps again. Apple has given developers the ability and right to change your phone with forced updates that remove features, trash, or remove apps. I did not approve them to update, or change any of my apps yet half of the apps that I had are broken or have changed for the worse, after their most horrible updates in years .

I bought another iPhone (mistake), it wants to force an update to restore my backup.

I need to be able to update to 14.4.2 from 14.2 is that possible?

[Edited by Moderator]

What version of iOS is it currently running?

What do you see when you go to Settings>General>Software Update?

What is the model number displayed in Settings>General>About>Model?

Sorry? If it's running 14.6, how can it be trying to install 14.6?

If it is NOT running 14.6, try updating using your computer instead of over the air.