How do I remove the battery from the engine bay of an 02 Vauxhall Corsa SXi?

I need to replace the battery in a 2002 vauxhall corsa SXi. I've removed the battery leads and the clamp that holds the battery to the shelf. However, there is a plastic sill above the battery that prevents me from removing it from the car. Does anyone know how to get the battery out of the car?