A group will only show within 'Manage table layout' whether it contains categories or not, similar to below.
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 categories contained in the group. The categories will revert to showing individually in the cash flow.
If you're looking to edit the actual categories, not the group, check out how to here.