You have a fundamental misunderstanding of your equipment.
When a lens is marked, for example 55-200mm f / 3.5-6.3, this means that the maximum aperture that you can use is f / 3.5 at 55mm and f / 6.3 at 200mm.
You can always stop at any other stop f smaller *.
** within the limits of reason here. The reason being the physical limitations of your goal. For many SLR lenses, this is the f / 22. I've had a Sigma once go to f / 32. Smaller than it's ever seen in the 35mm space.