Have changed my mailaddress. How to change in new computer, iPhone, Apple-ID

My provider have given me a new mailaddress and now I bought another computer, MacBook Pro. I have to change mailaddress in both iPhone and Apple-ID. How can I do that?

I created a new Apple-ID account and now I have two!!??

Where can I find instructions to change mailaddress in iPhone. How do I get rid of old Apple-ID?

The password to MobileMe have I lost long ago and can not find how to restall?

The same goes with the other solutions the Apple provide iCloud etc.

How to erace and start over again?

I have my older MacBook active also!

Certainly a simple problem for many but.....?