Paula, I'm not sure what you are doing to make a dup record but to edit any data you just need to highlite the data then press delete or just start typing over the highlited info. Sometimes you may find the field will not accept a full line so you may need to F9 to save the info after the delete. The add the new data.
If you have two of the same person. You can delete one by bringing that person up and keying Shift-F9. You will be asked if you want to delete say yes and the person is gone. If you do much of this you need to run "Pack" to remove old unused data.