Neil, if it is a late model van then the window stay is a slide fit onto the window receiver.
There should be a small hole which you put a very small philips screwdiver or similar(watchmakers style) press to release and at the same time, slide the stay off.
thanks, i tried to look for something of that nature but it was raining at the time and my bi-focals were less that uselful. Will try again in the morning - its a 2003 avondale dart