A group (containing accounts or empty) will display within 'Manage table layout' and can be removed or edited from there.
To rename the group just click the group name to see the following popover.
To delete the group entirely, hit the trash can symbol shown towards the right of the row. This will remove the group and unbundle any accounts contained in the group. The accounts will revert to showing individually in the cash flow table.
If you're looking to edit or remove an actual account rather than the group, click here.