Porch Posts/Columns

How would I go about determining if my 4x4 front porch posts are load bearing? The home is a rambler and my porch is about 4 feet deep and is concrete. The roof covering the porch is the same pitch all the way from the top of the home. There are 4 posts across the length of the porch, but at least one I could just pull off because they don't have any weight on them. I want to put in 6" round columns to dress it up, but don't know if they need to be structural. Any advice would be greatly appreciated.