Visit the Moderated Groups page here: https://www.bigdgaming.net/account/moderated-groups/
NB: you must be logged into your BigD website account, the page will prompt you to log in if you are not already logged in.
Click 'VIEW' next to the group you wish to manage.
When you are in the 'VIEW' screen of the Group you wish to add a member to, start typing the name of the User you wish to add to the Group in the 'ADD GROUP MEMBERS' box. Click on the correct User name, then click the orange 'ADD' button.
When you are in the 'VIEW' screen of the Group you wish to remove a member from, scroll through the list and find the User you wish to remove, then click on the 'REMOVE' orange symbol to the right side.