Hi,
That's not something you can change with just options.
You'll need to edit the file "show_block_characteristic" via the menu Display>Viewsand modify the code which adds the columns to the table there.
However, if you want to have a list of "specifications" for your product, it might be more appropriate to create custom fields of the table "product" via the menu Display>Custom fields.
They will display one below the other, and looking at what you currently have on that page, it seems that it's what you actually want to use instead of characteristics.