Welcome to NeuroTalk:

To change your username ID you have to contact Chemar.
Only an Admin can do this task. Contact me or her by PM when you decide on a new name. I can forward the request for you if you'd like to PM me instead. We often change ID's for new members who pick a name that they feel is not appropriate or too public.

The signature function is not open to new members until they
pass a short probation posting time. So soon, you can try again and the function should open for you.