Hi Gill,
To change your user name, log in to the community and click on 'my account', which is located at the top right of the screen. This will take you to your details (address, email etc) In the 'user name' box, change this to your new name and click on the 'update' button. This should then have changed your name. Please check this by logging out and back in again. If you have any problems, let me know and I will have a look into it for you.
Kind regards,
Cheryl, your editor