If you look on our FAQ page you will see that this question is addressed there:
How can I change the information in my profile? [edit your profile]
It is your responsibility to keep the information in your profile up-to-date. You should especially ensure that your email address is kept current. You can alter any of the fields in your profile, except your username. Once you have registered your username, it becomes yours for life. In extreme circumstances, you may request that the administrator change your username, but she will require a very good reason to do so.
Edit your profile here.