How to treat a old swollen and bleeding ear piercing?

Sounds like: it is infected. If it involves your ear cartilage, you must treat immediately with removal of foreign body and antibiotics, or you will risk deformity. If it involves skin only, it is probably ok to leave it in place, but you might need antibiotics anyway. See your doctor before it gets out of hand.

Get eval: Check for signs of infection: ^'ed redness, warmth, swelling. ^'ed tenderness, pus, red streaking, swollen lymph nodes or fever. Recommend keeping piercing in place unless directed by Dr (if removed – drainage tract will close up w ^'ed risk of abscess formation). Call Dr for medical evaluation. Your Dr may prescribe oral antibiotics or antibiotic ointments to apply to piercing site.