Unfortunately user names cannot be changed. If you wish to change your user name you will need to create a new account with an email address you have not used previously with Cam4.
NOTE: Gold memberships are non-transferable. If you wish a new user name you will need to contact the billing processor and cancel the existing membership. If there is still time on that membership you will not be able to purchase a new gold membership until it expires unless a different credit card is used.