If you are registered, you get access to the members only section, can participate in the buy & sell second hand forum and last but not least you can reserve your preferred username before someone else takes it.
Without sounding too angst, MY GOD MICHAEL. Use your bloody eyes, there's a link at the bottom of each email with "Link to your email settings/user profile". Click on that and bloody well sort it out yourself. Do you want me to call your mum and she'll come around and do it for you ?