Hi,
I assume that your site is multi-language, and beside default (en-GB) you want to add Espanol (es-ES).
So you need install: Espanol language package for Joomla, Espanol language package for VirtueMart. If it is installed, just change to that language.
After install and change your site to Espanol language, the text "Sales Price", "Product Details", etc. will be translated.
In the case it do not translated, you can edit /language/es-ES/es-ES.com_virtuemart.ini and find and change or add this:
COM_VIRTUEMART_PRODUCT_DETAILS="Your new text here for product details"
...
COM_VIRTUEMART_PRODUCT_SALESPRICE="Your new text here for Sales price: "
If you do not want to setup multi-language site (still English) and just want to change some words, so you can edit /language/en-GB/en-GB.com_virtuemart.ini then find and change the text value:
COM_VIRTUEMART_PRODUCT_DETAILS="Your new text here for product details"
...
COM_VIRTUEMART_PRODUCT_SALESPRICE="Your new text here for Sales price: "
Thanks for using our products!