To manage an Email Distribution List, you must be the manager of the group. Find the group in your Outlook Address Book, right click, and do Properties.  You should see a button to ‘Modify Members’ – click that.  You can then Add or remove members.  If you click add, it will bring up the address book to find their account.  Once you finish making changes, click OK, then Apply to save your changes. I believe there can only be one manager for the list, so let us know if this needs to be adjusted.