The flu virus can last in the body for one to two weeks but the most severe of the flu symptoms should go away within 3 to 4 days after the onset of the flu.
You're no longer contagious with the flu after the fever is gone and you have no more pain without fever reducing and pain relieving medications.
So while the severe symptoms of the flu should subside within 4 days you may still have the symptoms of the flu such as fever, dry cough, muscle weakness, body aches etc for up to 7 to 14 days.
There's not much you can do to get rid of the flu any sooner other than stay hydrated, take fever and pain reducing medications and get plenty of rest.
Also wash your hands often to get rid of the flu virus germs that can be spread.