How do we get categories to drop open showing subcategories only

[weloveperfume.co.uk]

Hi hope someone is able to help, I am trying to get the Parent categories when clicked on not to open to new page but still require it to drop down and show all subcategories in left Category box.

The reason for this is we do not need it to open to the subcategories page in the main window showing all Product Cat images.

So in theory let say the category Ladies Fragrances would be a dead link but would still drop down and show all subcategories in the left box.

I appreciate any help trying to get this work
:-)