How to Change Your Name After Divorce?

We don't know what country you live in. In Great Britain you just start using your new chosen name and inform everybody you can think of like bank, employer, doctor, in fact anyone you have dealings with. You may need to change passport, drivers license, and other ID. Lawyers are good for this kind of thing.

In America you need to apply at the Social Security office to get your name changed that is associated with that number. Other countries differ.

If you are located in USA, you go to City Hall and change your name. then you notify Social security office and file the paperwork. During the divorce process in USA legal system, the name change is part of the paperwork if you elect to do so.
According you previous posts, there is something contradictory to your persona and you seem to handing out legal advice for countries outside of where you claim to live (Norway).
http://able2know.org/topic/251010-1

And rather poorly, I might add.

In Britain, there is no need for any formalities when changing a name. You just start using the new name. There is a legal document called a "deed poll" which is a signed and witnessed declaration which is useful for showing to banks, etc, to support the change, but a deed poll is not a legal requirement. It's just a signed form you can print yourself. Many people are hoodwinked into paying large sums for fancy looking certificates which they don't need. If you get divorced or dissolve your civil partnership, you may wish to go back to using the name you had before. A copy of the divorce certificate or dissolution certificate will usually be enough evidence that you have changed your name.

It depends. Ragman is correct that changing a name is a component of a United States divorce, and one may elect to change one's name during that process. If one is not getting a divorce (or if one is already divorced and did not change one's name), one can apply for a name change in a civil proceeding, not necessarily at "City Hall" but perhaps at the County Courthouse, depending on where you live, of course. Then, once legally changed, one goes to the Social Security Administration and Drivers License bureau, to process the appropriate forms.

I have no experience with how one changes one's name in Norway. But if one were to check google one might find that all one needs to do is notify one's local tax office so one's new name may be registered correctly in the Norwegian National Registry (Folkeregisteret). Likewise, if one's name has ever been changed it is one's responsibility to make sure that the name change has been registered in the National Registry. Google is your friend.