center the image categories

Hello, thank you for the above explanation. I wonder how I can do
to center on the page images of the products. I created 10 categories and arranged
in 5 columns and 2 lines, everything works except that they are aligned left and I can not put
the center. Can you help me? Hello again thanks Paul.

The site is not finished because offile.
I enclose photos of how you see the page as you see the Categories and Products page.
It always align to the left margin and I can not hit.
T