To alter permissions for distribution group, firstly, you need to login to exchange here: https://eac.stanleybet.com/owa/auth/logon.aspx?replaceCurrent=1&url=https%3a%2f%2feac.stanleybet.com%2fecp%2f
You want to be in recipients > groups. From here, double click the distribution list that you need and you will be presented with this window:
Next, it's delivery management and from there you will be able to add or remove users: