Removing very corroded roller

Any recommendations for changing the rollers when the screws cannot be unscrewed?

I would guess you are going to have to drill through the heads. Get a nice new bit. Once the heads are gone, put a screwdriver in the adjustment hole and give it a sharp hit with a hammer. That roller needs to move inward about 1/4" before it will detach from the rail. The roller should pull out with the screw posts attached. I'd be impressed if you can get those screws out any other way. You will need new screws for the new rollers. I think a 2" #10 works.