Where is my SubSurf button?

I’m new to Blender and 3d in general so this is a VERY basic question. I’m trying to get through my first modeling tutorial which requires me to use the SubSurf button but I can’t seem to find it anywhere under the mesh panel in the edit window where it’s supposed to be. I’m using blender 2.40 but am not sure for which version the tutorial was written. Any help would be greatly appreciated, as you can see I can use plenty of it :expressionless: .

F9, Modifiers.