1. Click inside the cell from which you want to remove the drop-down list box. Do not double-click, as this will take you into the cell editing mode; just use a single left click.
2. Select the 'Data' menu from the top menu bar, and then click the 'Validation' option in the menu that opens.
3. Click the 'Settings' tab in the data validation dialog box.
4. Click 'Clear all' and then select 'OK'. Your drop-down list will be deleted.