Replacing battery - 1979 MGB

I am trying to replace the battery on my 1979 MGB. I have disconnected the battery cables but cannot seem to get the battery out. Does anyone have any ideas or tips for getting the battery out.

Have you removed the battery clamps? Batteries are usually bolted in place so they don't move around.
Below is a link for the original battery hold down, #37
http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29069&SortOrder=39