Deep vein thrombosis left me with 1 blood clot in right leg-3 clots in lungs-have been on warfarin 4 years now. Is this safe to be on this..

Warfarin. Its her risk-benefit ratio, and the reason that you are on the medication chronically is due to the history of any pulmonary embolism. I would discuss this with your primary care Dr. or hematologist.
Warfarin duration. Depends upon the severity of your leg and lung blood clots , whether you have a family history of venous thrombosis, and whether the events were provoked by surgery or other factors or were spontaneous . Only your treating doctor can determine optimal duration of warfarin however . Warfarin, especially if well controlled , can be well tolerated throughout either long term or even lifelong.
Safer Than Not! A recurrent pulmonary embolus could be fatal so i would suggest that the risk of bleeding associated with the warfarin is much lower than the risks of recurrent clot. Possible alternative would include placement of a filter in your ivc which has its' own possible complications.