Updating Products with Options/Sizes/Colors using Import Feed


I'm able to update our inventory and prices using the import feed (admin panel>administration>import data>products>products). However, I'm having difficulties doing this for our products that have variants like sizes and colors. There's no problem with updating these products manually by setting the product price to 0 then put prices on each sizes/colors but I'd like to be able to update these products using the import feed. Is this possible? How do I do this? Thanks for the help in advance.