I have a 440QE and I believe (it has been AGES since I had this discussion so I am hoping that I remember correctly) that you should thread the thread through the hole in the bobbin finger and you can adjust the tension with the screw on the bobbin. However, it has been suggested that it is better to get use a separate case (the gold?) and adjust that tension just for the bobbinfill rather than adjusting and readjusting your regular case.
If no one else gives you the advice that you are looking for here, then I would go to the Bernina_Aurora group on Yahoo. There is a ton of information and help there.