changing current Pro account to a business account which can be shared by multiple users

@peteattfhn - Here are step-by-step instructions, copied from the support article.  If you are just trying to change the account name and add users, you should be able to go into the Account Management->Account Profile menu on the left side and rename your account, then go into Billing and Add licenses,  then you can invite others to your account and assign them their own licenses.