To remove sequence numbers from a file, click Source > Sequence Numbers > Unnumber or press Ctrl+Shift+-.
To indicate whether the numbers start at column 1 or column 72, click Source > Sequence Numbers > Start Numbering at Column 1. When this option is selected the Renumber and Unnumber commands modify the text in the editor between columns 1 and 6. When it is cleared, the commands update columns 72 through 80.