Thermostat replacement

[Cooooooper]

Evening all

I am changing the thermostat on my 2004 2l petrol Bongo as the old one was stuck open. I’ve got a new thermostat and gasket. I’ve drained all the coolant out. I’ve removed the old thermostat…. But the old gasket is stuck pretty fast onto either side of the thermostat housing (see attached). Anyone got any tips on cleaning the old gasket off please? I don’t want to go at it with sand paper in case I scour the surfaces but at the same time, it ain’t going to seal with all that old gasket on it. Anyone advice greatly appreciated.