Hello Angelo,
 
1, To fix z-index problem with lens zoom. Please try to go to venus theme control panel in admin, then add custom css code:
 

.product-options dl dt,  .product-options dl dd, dd.swatch-attr.last {
    z-index: auto!important;
}

 
2. To change color swatch image. Please try to follow the tutorials:
 
http://www.venustheme.com/configurable-swatches-guide-for-magento-1-9-1/
http://sherodesigns.com/tutorial-configurable-swatches-in-magento/