How to take care of a discharging lipoma with an opening?

Dear Doctors, I have a 6 cm dia lipoma which first appeared 40 years ago. 2 months ago a 4 mm opening appeared on it and began to discharge a smelly and yellowish substance. Now it has shrinked a bit. So, will it goes on shrinking and disappear because of the discharge? Is there increased chance of infection because of the opening? How to take care of the opening? What measures should be taken to avoid future problems? At present no pain and inflammation but a little itching sometimes. Thanks.