How do you replace this roller?

I've been searching all over for these rollers. I have one question and that is how do you replace them? They appear to slide into a channel in the window. I removed the screw in the channel but they are pinned in by 'bends' in the channel. How do I get them out and put the new ones in. I've attached a picture of the broken parts but you can see in the picture that they used a chisel or screwdriver to 'break' the channel and thus pin the rollers in a specific area of the window.