You don't. I also have a 230. It is a sealed unit and only a technician can open it. Your instruction book should have some instructions but you can't take it apart like you could with the older Berninas. I clean my 230 after each project. I take off the needle plate, then open the door and remove the bobbin and the unit the bobbin sits on. I use a brush to get the lint off of the teeth and anywhere I see lint. I also have a small vacuum attachment that sucks up a lot of lint you can't see. Then I put some oil on the end of a q-tip and run that lightly over the inside of the bobbin and around the bobbin case. I also use the oiled q-tip to lightly rub over the moving parts. My Bernina tech told me that when he does a clean he uses up to 4 different types of oil and that is why the unit is sealed. If you are having a problem you possibly have something jammed somewhere. Perhaps a small piece of a broken needle or thread. If you haven't really used it, you should be able to take it back and have it looked at as it should have been thoroughly checked and cleaned before you bought it. It's a good machine and you shouldn't have problems with it.