How do I update my Apple 6S to IOS version 13.0 or above. Currently I have 12.5.4 version

You don't have an iPhone 6s.

It says iPhone 6 Plus.

iOS 12.5.4 is the last update.

You can't go any higher.

As pointed out, if you have 12.5.4, you do not have a 6s.

Is it possible to change my ipad from an ios 12.5.4 to a 13.0 or higher?

If you have an iPad Air, Mini 2 or Mini 3........... Nope... not possible.