Group admins, from the group page
Group admins see an ( Edit group ) link next to the group’s name.

It opens the Edit tab with the same form used to create a group: name, description, image, category, tags and privacy. Change what you need and click Update Group.

To remove the group’s image, click [remove] next to it before updating.
Only the group’s admins see the link and the form.
Site admins, in the dashboard
Site admins can edit any group under User Groups, including its members: see Managing group members.
Get Started with the Best WordPress Membership Plugin Today
Connect, Manage and Build your Membership Site