Changing the structure
To change the structure of a table,
Open a table in Design mode.
(If you are working in a shared environment, you see a prompt to open the table exclusively. Choose Open Exclusive to open the Table designer.)
Make a working copy of the table (choose File|Save As and specify a new name for the table).
Change the field definitions you want. You cannot change the table type.
When you finish, choose File|Save. In addition to saving your changes, the Table designer also copies associated files (such as .MDX and .DBT files).
Note
Open the restructured table in Run mode to verify that your data is in the condition you want. If not, you can revert to your original table if you worked from a copy.