What can I do to pass a drug test in four days, when I smoke marijauna heavily?

Nothing. I'm not aware of any way to clear thc in 4 days after heavy use. Drug tests will be positive for weeks. Without getting into the pros and cons of marijuana, you need to think ahead if you have a drug test coming up.
Stop smoking... If you have a job that requires drug testing, really the only way to not test positive for marijuana is to not smoke marijuana. Perhaps this will slowly change as states legalize recreational use, but until then, it is hard. Good luck.