To use the product image zoom feature for the product images you create and publish at your Virtuemart website complete the following steps

1. Log in to your Joomla Administrator Panel and select Extensions -> Template Manager.
2. Click on a template name to open the template settings area and open 'Product Images Settings'.
3. Set ON for 'ON/OFF Zoom Images Script' option
4. Provide other settings to fit Zoom Image Feature to your needs

Now you need to set big image for your product in VirtueMart

1. Log in to your Joomla Administrator Panel and select Components -> VirtueMart.
2. Select Products -> Product on left hand side navigation or Products on Control Panel to open your products list.
3. Open a product you want to add an image for Zoom Image Feature and select 'Product Images' tab.
4. To replace existing product image scroll down to Upload File area and choose Replace option. Click Browse to select an image file for your product.