Hi,
That text is taken from Virtuemart language INI file.
You can change it from this file:
/language/en-GB/en-GB.com_virtuemart.ini
find this line:
COM_VIRTUEMART_CART_OVERVIEW="Shopping cart"
and change it to:
COM_VIRTUEMART_CART_OVERVIEW="Cart"
Everything will be set.
Regards,
Support