To edit a member or guardian, go to the group > Members and press the three dots next to the members name and Edit.
To delete a member, go to to the group > Members and press the three dots next to the members name and Delete. If you do this in the main group, the member will be removed from all subgroups as well as from the attendance history and events. If you remove someone from a sub group they will still be member in the main group. The member will only be deleted from the group you are deleting them from, not any other groups they are a part of separately.
(It's only the administrator/s of the group that has permission to make these changes)
How can a member leave a group?
Go to the group > press More and scroll down to Leave group.