There are several ways to delete data:
 

1. Select the data to be deleted, and select Delete Data Set or Delete Column from the Data menu.

or

2. Call up the Data Browser, highlight a column or data set from the list and click the trash can.

or

3. Click a column header in a table or select all the rows of a column and then choose Edit->Delete (or press the delete key).  The whole column will be deleted (not just the cell values).

This action can be undone by selecting Undo from the Edit menu.
 
 

See Also:
Creating and Editing Columns
Delete (Edit menu)