Toan is right, you can't do this. This is a system family. Revit has 3 main system family plan types for every level created: Structural, Reflected Ceiling & Floor Plan. You can see this when using the 'Plan Views' tool on the view ribbon. If you click 'Edit Type' for the view, you will notice "Structural Plans" is a system family. The default type rather confusingly is also called "Structural Plan". If you rename this type, Revit will immediately put the new name in brackets next to the system family name in the browser. eg: Structural Plan (Structural Plan Details)
To look at it another way, you are asking the equivalent of changing an RCP to a floor plan. Just need to be more careful about the family type you're in before drafting. I would also recommend renaming the default view type names so they all have bracket names. This creates consistency in the view titles when you create other view types.
hope it helps.
