Edit Existing Group Using Outlook Web App

Login to Outlook Web App at https://outlook.com/usm.edu.

Select the group to edit under "Groups" in the navigation panel.
Select the three dots under the name of the group, and select "Settings."

Select Edit Group.

Here you can adjust the settings of your group. You can use the members tab to add/remove users and set their permissions.

You can change the name of the group or the email address associated with it.

You can modify the description.

You can also set this group to allow non-members to email the group by selecting the option: "Let people outside the organization email the group."