How can I wean myself off the ventilator if I have copd?

Honest discussion. You need to have a candid talk with your doctor. You need to know where your lung situation stands, how to improve it, is it medically possible to get off the ventilator. Your medications might need to be fine tuned. Pulmonary rehabilitation should be considered.
You can't... A patient cannot wean themselves off a ventilator. A doctor, usually a lung specialist, needs to wean patients off ventilators as this requires intensive monitoring of the patient's condition. See your doctor for possible weaning!