To edit an existing query, right-click ON the query line, and select the Edit Locations option from the popup menu. This will re-display the Specify Query Locations dialog for that query. All of the parameters you originally selected when you added the query will be shown.
Editing a query simply means that:
You can select a different Generate Values option, or change the number of locations for generating the values.
Show or hide the display of values, with the Show Queried Values checkbox.
Show or hide the query ID number, with the Show ID Number checkbox.
The Edit Locations option for queries is ONLY available as a right-click option, it is not available from the main menu.