Debbie, If you haven't done any merges, you can also get rid of them this way: (After a new backup with a new name): Select Export > Partial > then use the relationship filter to select All, then change the relationship filter to All Related and click on Clear. At this point everyone who is not related to you should still be selected. If you click on Delete they will be gone.
If it worked, create a new backup with a new name. That way if anything goes wrong you can return to this point later, or you can return to the earlier point by Restoring that backup.
You can also use the deadly "select & delete" procedure for deleting entire family lines. But there is no "Undo" button. If you make a mistake the only way of undoing it is to restore a backup made just prior to the change.