Postgres question

When we run PgAdmin III, the "connect to server" box pops up with
the username already prefilled. This is disabled so we

Can not change it, we can only enter our id. How can we change userids?
Any help on this would be appreciated, thanks.

Statement of confidentiality: The information contained in this electronic message and any attachments to this message are intended for the exclusive use of the addressee(s) and may contain confidential or privileged information. If you are not the intended recipient, or the person responsible for delivering the e-mail to the intended recipient, be advised you have received this message in error and that any use, dissemination, forwarding, printing, or copying is strictly prohibited. Please notify The CCS Companies immediately at (617) 965-2000, and destroy all copies of this message and any attachments. You will be reimbursed for reasonable costs incurred in notifying us.
****************************************************************************************************