Harvesting the worm castings can be done in different ways, but the most popular two are Dump and Sort it and Side to Side Harvesting.
Dump and Sort it is done by first preparing new bedding Then, dump the bin material on a large sheet of plastic and place it under a bright light. Since the worms are very photosensitive, they will burrow away from the light. The top of the pile can be scraped off.
Keep scraping the worm castings until it has been harvested.
Side to Side can be Harvested by only feeding the worms on one side of the bin for a couple of weeks. The worms will all move to the other side. Then harvest the worm casting from the other side of the worm bin. Put new bedding on the harvested side and feed the worms on the other side for a few weeks. The worms will move to the new side so the remaining Vermicompost on the other side can be scooped up.