
Hi Fiona.
I haven't done this myself, so I've consulted a book (Compost by Clare Foster). She says that when the compost is ready, the easiest way to separate the worms is to move the pile of worm casts to one side of the bin and add fresh bedding on the other side. Bury a handful of kitchen waste in the new bedding and after a couple of days, the worms should have migrated to the new side leaving a pile of empty casts ready to scoop out.
Alternatively, she says, you can tip the whole lot out onto a sheet of plastic. As worms are sensitive to light, they'll burrow down so you get casts on top of the heap and tangles of worms at the bottom. Remove the casts, then put the worms back in the bin with new bedding and kitchen scraps to get them going again.
Hope this helps. The book may be in your local library. The ISBN is 1844034054