On way is to simply move the completed compost over to one side of the box, add new bedding and food waste in the space provided. The worms will make their way over to the new area and the compost can be removed as needed. Given time and if you require all of the compost, then dump the entire compost onto a large plastic sheet to separate the worms manually. Common problems include unpleasant odours caused by adding too much food waste and the box becomes too wet and oxygen is depleted. Stop adding food waste until the worms have broken down what is there and gently stir the content to add more oxygen.
Worms can crawl out of the bedding onto the sides of the box if conditions are unsuitable.
This may happen if you add too much citrus peels causing high acidity. Correct this by adding dolomite lime and limit citrus waste. Prevent fruit flies by burying food waste and not overloading. Keep a plastic sheet, old carpet or Hessian on the compost surface. This is a great intro to vermicomposting, Geoffrey.