Login to your admin area and go to Catalog > Products in your menu.
Click Insert/Edit (We recommend creating a test product first. Make sure the test product is working, particularly on the frontend, before changing all of your other products).
Click on the "Stock Control" tab. You should see what the below image shows.
Change the "Has Options" option to Yes - OpenStock, Another 2 tabs will appear called "Option" and "Option Stock".
Add your options and option choices, click save then go back into edit your product.
All of your available option stock choices will have been calculated for you and you can now add your stock, images, sku's etc.
