As administrator of an enterprise you are responsible for adding and removing users from your enterprise account. If you have upgraded from a Professional account to an Enterprise account, the users defined in the Professional account were all moved to your Enterprise account.

If your company uses an SSO application, like Okta, even better. Onshape works with other single sign on providers, too. See Configuring Integration with Identity Providers for more information.

For an additional Learning center resource, follow the technical briefing article here: Sharing outside an Enterprise (Onshape account required).