This feature is only available with a Pro or Enterprise Site Control account. Click here to upgrade your account.
If you signed up for a Pro Account, you can have up to 25 people in your Site Control account at once.
For Pro Accounts, just follow the process below to invite additional people to your account. If you need help setting permissions levels for new members, you can read about that in User Permissions.
To uninvite a collaborator, select “Remove from Group” from the User Permissions dropdown list.