To change the text strings used on the VirtueMart pages, such as the words used to label each of the prices, or used in the Ask a question link, you should use Joomla's Language Manager to locate the required string and set up an override.
http://docs.virtuemart.net/tutorials/33-templating-layouts/107-customization-of-displayed-text.html
Tutorial on language overrides: http://www.ostraining.com/blog/joomla/languge-manager
There also is a tutorial now in the tutorials section at virtuemart.net: http://docs.virtuemart.net/tutorials/33-templating-layouts/107-customization-of-displayed-text.html (http://docs.virtuemart.net/tutorials/33-templating-layouts/107-customization-of-displayed-text.html)
it may also help to read some basics first http://docs.virtuemart.net/manual/general-concepts/214-multilanguage-and-multlingual.html