You mean that you want to display the big version of the image on mouse over instead of when the user click on it ?
You can do that by editing the file administrator/component/com_hikashop/helpers/image.php near line 130. You can replace the code
$html = '<a rel="{handler: \'iframe\', size: {x: '.$this->width.', y: '.$this->height.'}}" target="_blank" href="'.$this->uploadFolder_url.$path.'" onclick="SqueezeBox.fromElement(this);return false;" '.$optionslink.'>'.$html.'</a>';
by the code
$html = '<a rel="{handler: \'iframe\', size: {x: '.$this->width.', y: '.$this->height.'}}" target="_blank" href="'.$this->uploadFolder_url.$path.'" onhover="SqueezeBox.fromElement(this);return false;" '.$optionslink.'>'.$html.'</a>';
Please note that this modification will be overwritten if you update HikaShop.