Perform the following steps:
Choose Tools -> Filters.
From the drop-down list at the top of the Filters dialog, select whether the filter that you want to edit is for incoming or outgoing email.
Select the filter that you want to edit, then click Edit. An Edit Rule dialog is displayed.
Modify the details of the filter in the dialog as required. For more information about the dialog, see To Add a Filter.
When you have modified the details for the filter, click OK on the Edit Rule dialog.
Click OK to close the Filters dialog.