Facebook extension [help!]?

[Conflict]

Hey, I was wondering if anyone could help me with some stuff on facebook, recently my friends have recieved a message from facebook saying they can add "/*insertnamehere" extensions like myspace do.

e.g. http://www.myspace.com/adumz

But I'm unable to find the link to make my facebook:

http://www.facebook.com/adumz


a link to the thing that allows you to edit it will be much appreciated, or a guide.

thanks x

[Link-DS]

Here: http://www.facebook.com/username/