Spreadsheet App question - how do I delete a column name ?

[Michael de Estrada]

I have a saved spreadsheet where I named several columns, and now I want to delete the names and revert to the default names, ie. A,B,C etc. I can change the names easily enough, but there doesn't any way to delete them. If I attempt to enter the original names such as A,B,C etc, or if I attempt to delete the current name and enter a blank line I get an error message "invalid input". I can delete the spreadsheet, but cannot reset it. Any ideas ?