The person who originally created the retailer in the TEST1 or TEST2 system is regarded as the administrator. It is up to him or her to create new user accounts (and, perhaps, making you an administrator too). This is achieved in the Delivery Manager application itself, in the Setup area.

When the user account is created, ensure you use the same email address as you have in the Development Centre. That way, your account will be listed on this page. You should also ensure the user account has the right to access the system using web services ("May access the webservices API").

There is nothing to stop you from sharing your security credentials with your colleagues if you so wish.