To clean: clean with water and Scotch Brite Dobie all-purpose cleaning pads or any plastic pad that doesn't scratch the glass. Can be bought at supermarkets or Lowes stores.
Winters below 32 degrees: the birdbath tops can't stay out in winter temperature below 32 degrees with water inside. They can be brought inside or left outside in a covered area like a porch with no water in the bowl. Or put a plastic bucket inside the lid of the birdbath and cover with a large plastic bag so water doesn't collect in the bowl.