You can't, unless made some custom coding changes on PHP files under this folder:
ROOT//templates/YOUR_TEMPLATE/html/com_virtuemart/cart/
But since it is a custom modification, it is not covered under our "free support".
If it was an easy task to do, i would try to assist you. But it is not. You will need to spend some time on it and re-design the entire shopping cart page.
Regards.
Support & Development