You will give yourself the best chance of shifting them if you clean out the screw head as best you can. Then use a good condition screw driver of the correct type (No: 2 Pozidrive).
If this fails, Mole grips might work. Lastly drilling the heads off is the way to go.
Cut a slot and use a flat blade, the heat seems to slacken the screw as well.
Hi Nodge. Cheers mate. I cleaned the all out with WD40 and let them dry. I got the driver in but the screw disintegrated around the driver. So still no luck. I think I will try the dremmil. Where can I get replacement screws from as these ones are totally finished.
Kind regards
Kieran.