You might have noticed that by default, it’s impossible to change the attribute set of a product, once it has been added to one. At first you don’t even notice this, but once you want to change the attribute set you find out it’s impossible. It seems very strange that this is not possible in Magento, luckily there is a community built solution for this issue!
To modify a products attribute set, just follow the following steps. First search for ‘flagbit change attribute set’ on Magento Connect, or using Google. Don’t feel like searching? Just use this link: http://www.magentocommerce.com/magento-connect/flagbit-change-attribute-set.html
Download and install the extension first. After that you will be able to change the attribute set of a product through the product list page in the Magento Admin environment.
Dead simple and very useful!