Yes, you can change your 3 additional coworkers at any time. Just log into your account and click on "add your free members".
When an administrator removes a coworker, the coworker will no longer have access to the membership items but they will retain their individual CharityHowTo account and any individual purchases they have made outside of the membership.
You can access your Membership settings in your CharityHowTo library at this link: http://www.charityhowto.com/library
If you need to you can set a new password at this link: https://charityhowto.com/user/forgot-password