To drop a column in a table, you can either :
1. Select the column of a selected table in the Object Browser and select Others -> Columns-> Drop Column. A message box appears. Click on Yes to drop the column(s).
2. Right click on the table in the Object Browser and click on Alter Table in the drop down menu or press F6 to alter the highlighted table. Click on the check boxes beside the column name of the column(s) you wish to delete. Then click on the (-) sign in to tool bar(the delete button) to delete those columns.
If the columns are referenced by any index or foreign keys then a warning message wil be displayed as shown below. On YES, it will modify the corresponding index(es) or foreign key(s).