How to modify categories view in virtuemart?

In virtuemart forjoomla 1.5 , the category view is difficult to find out where to modify. Specially, the default number of columns is 4, and now you want to change to 3, you don't have any option to change. I have taken all day to find out where it is and how the virtuemart runs.
Firstly, the home page of virtuemart is set by the file administrator/components/com_virtuemart/html/shop.index.php, and the template is components/com_virtuemart/themes/default/template/common/shop.index.tpl.php. For example, if you don't want to display categories view at the front page you can delete
echo $categories at line 7.
You can read more How to modify categories view in virtuemart? at jw-extension.net